Mms: Use a more familiar 'mark as read' icon

The existing 'mark as read' icon is a bit confusing and doesn't make clear
where it is for. This commit replaces the existing cion with the read icon
which is used in Email and Gmail.

Before: http://goo.gl/GXKfj
After:  http://goo.gl/RTEwa

Change-Id: I3c7ae7aa6173e29e687a7e0d564b2d54fcc61a51

Conflicts:
	res/drawable-xhdpi/ic_menu_done_holo_dark.png
Mms: Updated 'Mark as read' notification action icon

Users still think the 'Read' action means 'to read' (sounds like reed)
rather than 'the message has been read' (sounds like red).  This new
icon is an attempt to clear up the confusion and replaces the email
looking icon currenty in use by something a bit more suitable for the
Mms app.

Drawable curtesy of Björn Lundén

Screenshot:
  https://dl.dropbox.com/u/50993944/Screenshot_2013-04-08-18-16-03.png

Change-Id: I890a99c76173dfcb1179fea8ef80d24ecf5133ac

Conflicts:
	res/drawable-xhdpi/ic_menu_done_holo_dark.png