Fist cut of nested folders

1. Rename FolderListFragment.FolderListSelectionListener to
   FolderSelector.

2. Allow special views to be tapped; all existing special views
   disallow taps.

3. Allow nested folders in ConversationListFragment. The adapter is
   responsible for populating the nested folders above the
   conversations.

4. Add a nested folder special item for the conversation list. This
   reuses current resources and is particularly ugly.  The ugliness
   will be fixed once we have a UX spec and real assets.

5. The child folders are loaded through an ObjectCursorLoader in the
   ConversationListFragment.

Change-Id: I5eb566d7a1f87c1a11fc6961378d00650a27007d
17 files changed