Feature/remove piston

I've rewritten the collection_catalog app to not depend on any external libraries.  This removes the requirement for django-piston, and subsequently diff-match-patch and httplib2. 

The admin was also broken, depending on a custom widget for a ManyToManyField that has suffered from bit rot.  It turns out that the admin can be coaxed into providing searchable fields without a third part widget.

This was basically a friday morning warm up exercise, which I may do more of in the future to address code quality issues.