Major refactor of ConversationCursor

* ConversationCursors are now associated with a particular loader;
  there are no static methods or static state fields
* ConversationCursorLoader maintains a list of current loaders
  (for tracking/debugging)
* AbstractActivityController acts as a router of conversation
  changes to/from fragments (currently message view -> conversation
  list)

Change-Id: I0eb554615b4bf93b3547ff28e2bd5913e8703a97
21 files changed