Fix misuse of super
Add ReviewedVersionTracker
Ensure that ForeignKeys to proxy models work

Also gives ReviewedVersionTracker the right app_label
Add interface for review queue
Add view_instance property to widgy views

This gives us an API for widgy's authorization framework.
WidgySite.authorize needs a view instance, so we need to know the view
instance from the view callable.
Enable the review queue on the demo site
Add Api tests for review queue
Add SCSS file for unapproved_commits admin layout
Fix layout for Review Queue
Add widgy siteperms template tag

This allow us to access WidgySite.authorize framework from the template.
Major refactoring of review queue

Pulled out from core and put into its own contrib app.

Signed-off-by: Antoine Catton <acatton@fusionbox.com>