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
Merge branch 'cm-11.0' of github.com:CyanogenMod/android_packages_apps_Mms into cm-11.0