Workaround for featured asset race condition

The previous workaround was not working on non-local machines.
The ``fileupload`` signal is also no longer required.
Explicitly pass changed event to callback
Set Tastypie dependency version

Set the Tastypie dependency verison to before backward-incompatible changes
were added.
Merge branch 'develop' of github.com:PitonFoundation/atlas into develop
Fix typo

The commit SHA was wrong for the required commit of django-tastypie
Test for automatic featured image selection
Listen to "change:status" not "publish:story"

Defining a custom event on the event bus isn't neccessary because the
"change:status" event is triggered on the story model when it's
published/unpublished.
Fix display of sharing sidebar

The toggling with story publish/unpublish got broken in previous commits.
Remove debugging statement typo.
Use the sharing widget in the builder

Instead of the specialized (and broken) sharing interfaces in the
Publish/Share step of the builder, use the share widget used elsewhere in
the site.  That gives us a single point for improvements to the widget.