During the registration and in dashboard, the new password is required
to have min 6 characters and not be in common passwords. Those rules are
not enforced when changing password in the account section or resetting
password.

Extract password validators into core validators as they are used by
multiple apps. `password_validators` now contains all validators applied
to passwords: DRY principle.

Changed auth tests to have a proper password for password reset.

- Use a FormView (as it is a form view)
- Move the redirect URL validation into the form

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.

* Emailbackend: Updated to use REQUIRED_FIELDS
* Demo and sandbox site now use compat.AUTH_USER_MODEL as well
* Added example custom user that gets tested for Django >= 1.5

Before it was lower-casing everything first which prevented users being
able to login if their email address contained capitals.  We now only
lower case the host part as this is case-insensitive.

Fixes #505

A basic security measure to ensure a user is aware if his/her account
gets compromised.  The email contains a link to the password reset form
which allows a new password to be set.

Fixes #436

Fixes #376

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

With complete webtest for password resetting story.