This was a code change introduced in the refactoring, but does not make
any sense. Luckily, it also caused the tests to fail, so I'm happy to
revert it.

This allows updating code in both places, if necessary. Getting Django
1.5 support would be painful otherwise. This also removes the circular
dependency of django-oscar-testsupport on Oscar.

The requirements were merged. The imports were updated
accordingly. Unused imports in the touched files were removed. No
further changes.

The AccountSummaryView was trying to do too much and included random
bits from the other views. It has been changed to a simple
RedirectView. The redirect target can now be set with
OSCAR_ACCOUNTS_REDIRECT_URL and defaults to the newly-introduced
ProfileView. This leaves the UX unchanged apart from the fact that
was used to be scripted tabs is now separate views.

There was a lot of template duplication between the separate views. I
have introduced a PageTitleMixin and used this to significantly reduce
redundancy (e.g. hundreds of lines). This also led to removing a few
slight inconsistencies regarding headings, breadcrumbs etc.

The new templates have been categorised in subfolders.

Apart from the new ProfileView, I've had to introduce a simple
ProductAlertListView. I've also upgraded the ProductAlertCancelView to
be useful for both canceling from emails etc. as before, but also from
the ProductAlertListView.

Fixes #376

* 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.