Refs #2567 - the changes made there fail if the stock record
belongs to a child product.

There is a subtle change in behaviour here. Null is converted to ''
only when reading the field value from the database. Previously
this was done in the to_python method, but this causes problems
with uniqueness validation.

* Silently skip stock allocation manipulations if the product class doesn't track stock.

* Make it possible to cancel/consume stock allocations without line args.

You can now do:
consume_stock_allocations(order)
cancel_stock_allocations(order)
without the lines / line_quantities arguments.

Previously, validation did not pass when current locale is "en-gb" and URL is "/de/catalogue/" and visa versa due to default Django URL resolvers behaviour  - they do not take into account all locales, only current.

Fixes #2526.

phone_number_fields is more correct grammatically.

Add to the dosctring for the class, and display it in the documentation.

With this change phone numbers (any qty) can be added as `ModelForm`
property `phone_numbers_fields` - dict where "keys" are names of
phone numbers fields and "values" are attributes of fields.

* `PhoneNumberMixin` clightly reworked and moved
from `oscar.views.generic` to `oscar.forms.mixins`
* Couple tests added (based on previous tests)

If a url_name is invalid, then log the exception instead of silently discarding that menu item.

Notification subjects have a max length of 255 characters, which can easily be exceeded by long product names. Change the alert logic to provide a short notification subject and put the longer content in the notification body.

This patch also modifies the notification utils to make it obvious that the positional argument is a notification subject, not a body.

* flesh-out initial opaque data-model

refactors the basket line consumption into a facade object.

the goals is accomodating combitions of various offers on the same basket-lines,
while remaining backward compatible with the current single offer per line
policy.

* add docstrings

* add exclusive flag to conditionaloffer model and continue refactoring

* test new offer consumption on basket view

* cleanups

* fix exclusivity

* code style

* add cast to pacify tests

* spelling

* add some documentation to the release notes

* move documentation to new 1.6 release docs

Fixes #2414.

This reverts commit 9f74ef94e7. The related bug was fixed in Django 1.11.4

Subsequent views of the page (for the same order) should not trigger an event.

Fixes #2413.

- When tax is known but zero, line_tax should return Decimal(0).
- When tax is not known, line_tax should return None.

Fixes #2395.

* Add datetime attribute to ProductAttributeValue as asked for in issue #2389

Used widget DateTimePickerInput from oscar.forms.widgets

* Fix migration catalogue 0012 (was error with python3)

* Add tests for ProductAttributeValue

In Python 2, adding None to the basket total worked, but in Python 3 this raises a TypeError. This fixes the handling of totals to distinguish between a zero price and a non-existent price.

* fix bug in grouped_voucher_discounts

* add test for grouped_voucher_discounts

* remove 3.6.1 syntax

* improve test

- Refactor clean methods to return all validation errors, rather than just the first one we found.
- Fix clean method type errors in Python 3
- Add tests for the clean methods for all benefit types.

Fixes #2277.

- If start_datetime is null, then the offer has no start date.
- If end_datetime is null, then the offer never expires.

Use the ActiveOfferManager in Applicator.get_site_offers instead of
reimplementing the same logic there.

Fixes #2344.

Also remove some Django 1.6 compatibility code.

Fixes #2176.

Django 1.9 introduced the AUTH_PASSWORD_VALIDATORS setting which allows for
more flexible password validation. Switch to using that when it is available,
with a fallback to Oscar's previous behaviour in Django 1.8 or when this
setting is empty.

This was removed from the parent class way back in Django 1.4, and was
not being used at all here. It existed only for backwards compatibility.

Fixes #2168.

Now after ConditionalOffer deleted will be deleted related Benefits and Conditions models (through post_delete signal) if they are no longer used by other offers (with exception of custom benefits/conditions). Plus some small changes related to PEP8 and typos.