Implement SMS mark for unread (Cyan-348)

Change-Id: I999e4159603d13062b535b2445cbc7efd3cf9b7b
Mms: Move Mark as unread strings to the correct places

* Strings go to cm_strings
* Plurals go to cm_plurals
* Fixed plurals for CM standards

Change-Id: I7227c27039188202b376ecf50d79c9918c3b456a