Mms: Use a card-based UI

Before: http://imgur.com/7DpIenj
After:  http://imgur.com/H8FmJjN

PS9:
- Remove top and bottom padding in converation list
PS12:
- Add padding again but it will scroll now.

Change-Id: I798502ba1a19f8dcb271627ba3af83922ace2cf8

Conflicts:
	res/layout/conversation_list_screen.xml
	res/values/colors.xml