This allows admins to:

* Preview emails in the dashboard
* Send preview emails
* Save emails

Fixes #359

This involves various template changes to adapt to new bootstrap.

Also:

* New responsive sheets and added responive classes into templates
* Add navigation to accounts section
* Simplify product listing templates
* Product lists enlarged images
* Single promo in the side bar
* Add btn-full for button full width responsive
* Checkout nav slightly adjusted
* Add responsive nav into the accounts
* Correct CSS class-name typo
* Make empty basket message a bit more sensible
* Remove in-page link to product description
* Widen price columns on basket/checkout as some currency symbols start
  wrapping
* Add whitespace to detail page availability messages
* Remove snowcone from project

Issues:
Fixes #351
Fixes #349
Fixes #345

Consumption now sorts the basket lines in descending price order so that
the most expensive products are consumed first.  This means that
multibuys apply in a more natural way.

Fixes #348

The OrderDiscount did not store (a copy) of the offer
name within a separate field which causes an issue when the
offer is deleted. E.g. it breaks the order history view for
the customer because no offer data is available.

I have added a new field to OrderDiscount that is automatically
populated from the offer.name field. This works in the same way
as voucher_code does in the same model.

I also found two issues with the voucher implementation within
the same model that are fixed now.

Fixes #330

A user in Oscar is identified by email address instead of the
username. This is, however, not set as a ``unique`` constraint
in the user model in ``django.contrib.auth.models.User``. Checks
if an email already exists are carried out when a user registers
but are ignored when a registered user changes their
profile. This can lead to multiple users having the same email
address which should not happen.

I provide a failing test with a mixin that can be used in both
the ``UserForm`` and ``UserAndProfileForm`` to clean the email
field when validating the form. A ``ValidationError`` is raised
when a user with this email address already exists and is not
the currently edited instance (makes sure that profile updates
with unchanged email work still).

Fixes #324

* They are now known as 'stock alerts' instead of notifications.
* They have been moved into the customer app largely (instead of their
  own one).
* The model implementation has been simplified.

This is a squashed, rebased version of the original branch.

Original commit messages:

* product notifications are visible *only* if a product is not in stock
* or does not have a stock record (a new product).
* an anonymous user can sign up for a notification of a product. They
* receive a confirmation link that they have to open to activate their
* sign up. An anonymous user does not have any means of managing their
* notifications in a list. The confirmation email contains a second
* link, however, with a *unsubscribe* link that allows for disabling of
* the notification.
* a registered user can sign up for notifications without having to
* confirm it. When a registered user signs up for a notification, the
* "Notify Me" button disappears from the product information and is
* replaced by a note stating that the user has already signed up.
* registered users can manage (activate/deactivate) their notifications
* in their account settings.
* an anonymous user that has signed up for notifications and creates an
* account will pull in their notifications and have them assigned to
* their account and are then no longer marked as anonymous
* the notifications app registers a receiver for the ``post_save``
* signal of ``StockRecord``. Whenever a stock record is updated, the
* notifications are checked for this particular product and emails are
* sent out. These notifications are then disabled (not deleted) and
* marked with the date the email was sent. This hides the message from
* the registered users account. Notifications are still accessible,
* however, for staff members in the dashboard
* In the dashboard, the ``Customers`` navigation node is extended with a
* ``Notifications`` child that allows for editing, deleting and viewing
* all notifications. It also provides filtering capabilities for them
* based on status, customer name, customer email and/or product keyword.

So we add handling to the filter where we check the value can be
converted to a valid decimal.  If not, return an empty string.

Fixes #316

Plus fix a bug when handling None.

The previous UPC validation in ``ProductForm`` broke updating the
a product. I realised this while digging around to fix the broken
``StockRecord`` issue that broke the CI build.

The validation now uses Django's validation of ``unique`` fields
instead and works.

The ``StockRecord`` issue was related to creating a form in the
update view providing stock record data in POST with ``partner``
empty. I corrected that and added a test case for it.

Attempting to create a new product with a UPC that already exists
raises an ``IntegrityError`` instead of handling the ``ProductForm``
as an invalid form with an appropriate ``ValidationError``.

I fixed that by adding a ``clean_upc`` validation method to the
form by checking for an existing product by UPC. I am not sure if
that is the most efficient way to validate this. If there's a
better alternative, I am happy to change it...and learn something
:)

**Note:** I switched the functional tests in ``product_tests.py``
to use ``WebTest`` while I was at it.

Added new field to offer that allows their max num applications to be
controlled.  Dashboard adjusted to support this too.

This fixes a bug with adding customised products to the basket, where
the clean method would get a MultipleObjectsReturned exception as the
lookup wasn't taking options into account.

Also fixed a display issue with required options in basket forms.

It's potentially confusing to have it default to a value as you might
miss this in your project.

This involves:
* Better checkout templates
* Updated availability logic for products with no stock
* Updated dashboard templates

* New attribute on product class
* Optimised checkout for digital goods

This is a major clean-up of offers, tidying up the implementations and
rewriting the test suite.  This should also clean up some edge cases
around the use of max_affected_items.

* replaces all occurences of ``datetime.now()`` with
    ``django.utils.timezone.now()`` which returns aware or naive
    datetimes based on ``USE_TZ``
* increases ``South`` version to 0.7.6 in dependencies to make
    aware datetimes work in migrations.
* Oscar's sandbox is now configured to use aware timezones by
    default

* Tests now split into more coherent modules
* Added IDs to forms to help WebTest
* Some refactoring along the way

Turns out this is a bit confusing.  Better for it to do nothing by
default and this behaviour can be enabled when it is needed.

Change to products URL was not picked up here.

With complete webtest for password resetting story.

Now using --spec format which is more readable (most of the time).

ListView doesn't make sense when you are not paginating

They weren't applying to lines properly.  Fixed with test.

This view has a form that assumes anon checkout is allowed, which it
isn't always.  Treating it as a special case was causing it to be
displayed when it shouldn't.