Fix validate_payment_event for payment events with no lines specified

Unavailable product bug fixes

In Range.contains_product, use get_product_class().id instead of product_class_id

Remove unexisting JS method call from dashboard order list template

Fix voucher expiration message

Fix indirect update of session data, fixes #1865

Typos

Register BillingAddress into django admin

Some review form fields do not always exist

Added options attribute addition documentation

I was tasked to create a product that would be out-of-the-box available to our users, so I added the attributes in a data migration but I had a hard time finding any resource that describes adding options via code and had to dig through Oscar's code on GitHub to figure this out. People would benefit from an addition like this, at least save time from digging through code to figure this out.

For logged in users, the `name` and `email` fields do not exist in the form. Currently Oscar still tries to render them which results in empty and invalid form inputs being generated.

Correct allow_failures for Travis

The deprecation error for inspect caused travis to fail. Django 1.8
will get official support for Python 3.5 in a later patch level release

See https://groups.google.com/forum/#!msg/django-developers/JlkwHprjqJc/kEaZyAOxDQAJ

Small typing error.

Fix dashboard overriding alert style

Django 1.8 supports Python 3.5. It does raise a DeprecationWarning,
which is safe to ignore. We only care about DeprecationWarnings in our
own code.

And it seems that Travis wants all allowed failures listed explicitly,
so we do that. It should now pass again.

As part of my last PR, I had USE_LESS enabled for testing purposes and
accidentally committed the setting. By default, we don't want to run the
(somewhat slow) pre-processor!

Update templates so that the product title isn't automatically escaped.

Fix create_line_reference for options already enconded to utf-8

Django 1.9 support

In Django 1.9 the FormView.form is added via get_context_data(), make
sure we call this in CheckoutSessionMixin.get_context_data()

The debug-toolbar-template-timings-panel isn't compatible with 1.9 yet

 - Set Meta.app_label on models created in the tests
 - Use logging.NullHandler instead of django.utils.log.NullHandler
 - Use oscar.core.loading.get_model() instead of django's get_model
 - Remove template tags '{% load url from future %}'

In Django 1.9 the decorator from six is used so simplify the test to
just check for a __unicode__ method

This is required in Django 1.9, see
https://docs.djangoproject.com/en/1.8/topics/auth/default/#session-invalidation-on-password-change

Remove django-compressor

django-compressor used to trigger processing of the less files during
development. But with the browser-based compiler, an easy replacement is
available. This even lowers the barrier to altering styles, because
getting npm up and running isn't required.

Offline compilation isn't impacted.

Using the most current less version seems to not cause any trouble, so I
removed the version requirement.

django-compressor served it's purpose, but given the advent of
more and more frontend JS work, and the accompanying build tools (grunt,
gulp, etc.), it makes less and less sense to use compressor. Jannis
Leidel himself also stepped back from maintaining it.

In my experience with Oscar project, it has also become a bit of a
liability to have compressor as a dependency. Most projects don't use it
any more, but it's not easy to disable/override because all our
templates include it.

So, let's keep things simple and remove it as a dependency. That paves
the way for using other tools, while it's always easy to add back.

Use class=text-right instead of inline style.

Update templates with .icon-warning to .icon-warning-sign.