Throttle the folder loader updates

With large batches of operations, the state of the folder
changes a lot.  This causes a lot of update in the ui to update
the unread count.  Instead delay the updates of the loader for
500ms from the last call to onLoadInBackground()

Change-Id: I7e7872e5888c74965fd9ca1a86c668cee5a79387
2 files changed