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

Change-Id: I845598bb706089c788e8d829d7d4ebfb7928eb73