put signOut in an AsyncTask and show a ProgressDialog
use the asyncSignOut in WPActionBarActivity
use the asyncSignOut in PreferencesActivity
don't send BROADCAST_ACTION_SIGNOUT from removeWpComUserRelatedData()
null check mProgressDialog before dismiss and use local context instead of getContext
Merge pull request #1895 from wordpress-mobile/issue/1796-signout-lag

fix #1796 signout lag