OmniSwitch: quick switcher

-added back button support
-added quick switcher settings
-added quick switcher button config

PS10:
-fixed division by zero - thanks Juan
-added item limit preference

PS11:
-quick switcher depends on drag handle
-fix drag handle switch
-next try - division by zero fix - thanks Menno

PS12:
-fixed timing issue - thanks Cory

PS13:
-added showcase for quick switcher
-remove start and stop service broadcaset and
INTERACT_ACROSS_USERS_FULL permissions since we dont
need it anymore with the simplified recents integration
requires https://gerrit.omnirom.org/6953
-listem to ACTION_SHUTDOWN intent to save local prefs
-fixed back key handling

Change-Id: I845598bb706089c788e8d829d7d4ebfb7928eb73