Jelly: Implementing favorite management through a ContentProvider.

Inspired by the history ContentProvider. Previously database
queries were being invoked on the UI thread. This is no longer
the case. Edit and delete favorite were also taken into account
and even the delete animation is working like before.

Edit, Add and Delete actions implemented as static inner
classes to avoid implicit activity reference. May otherwise
cause memory leakage.

Snackbar parent view is referenced as weak to avoid potential
illegal state exceptions.

Change-Id: I214ec25a90e86048da0e97be62f899d0af99c1a0