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>

Change-Id: I95fac793abdc2c9c81cf6b21d69b8f6dba000500

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