Resolve removed 'AUTH_PROFILE_MODULE' setting

The 'AUTH_PROFILE_MODULE' setting, and the 'get_profile()' method on
the 'User' model are removed in Django 1.7. This causes errors when
using Patchwork with Django 1.7+.

There are three changes necessary:

 * Replace profile model's 'ForeignKey' with a 'OneToOneField'
 * Remove all 'get_profile()' calls
 * Delete 'AUTH_PROFILE_MODULE' settings from 'settings.py'

These changes are discussed here:

    http://deathofagremmie.com/2014/05/24/retiring-get-profile-and-auth-profile-module/

Django 1.6 also introduces two other notable changes:

 * The 'XViewMiddleware' module has been moved
 * A new test runner has been introduced

It is not possible to fix these issues without breaking compatibility
with Django 1.5. As a result they have been ignored and must be
resolved in a future release.

Signed-off-by: Stephen Finucane <stephenfinucane@hotmail.com>
Signed-off-by: Jeremy Kerr <jk@ozlabs.org>