Added option to show full datetime for messages

PS2: clean up

Signed-off-by: Dirk Rettschlag <dirk.rettschlag@gmail.com>
Signed-off-by: Stevespear426 <stephen.k.spear@gmail.com>
Signed-off-by: Andrew Warfield <hiasant@gmail.com>

Conflicts:
	res/values/strings.xml
	res/xml/preferences.xml
	src/com/android/mms/ui/MessagingPreferenceActivity.java

Change-Id: I26dae26ed9f8c4502bb0503915454f229eca4a2a