Mms: Add close button for removing subject as a new UX path instead of relying on the depracated onKeyListener

- Vector FTW

Conflicts:
	res/values/cm_strings.xml
	src/com/android/mms/ui/ComposeMessageActivity.java

Change-Id: I69b1b95cd01f38d3801e33eff6a3dd9c4941fab6