Play sound at half-volume and dont show notification for new msgs in current thread

cherrypick from https://www.codeaurora.org/gitweb/quic/la/?p=platform/packages/apps/Mms.git;a=commit;h=c8d727902ff6976c45285a12aab176545a7848bb

Conflicts:

	res/values/colors.xml
	res/values/dimen.xml
	res/values/strings.xml
	res/values/styles.xml
	src/com/android/mms/ui/ComposeMessageActivity.java

Change-Id: Iedda9c4d5d48e24037fa4252f4d0fe233563e7a3