talkback: Reset to 0e64bcd5357619dbb4378fa3abd714537947b915 and localize
talkback: fix line breaks before all messages
talkback: cleanup (remove one excess tab)
talkback: cleanup

Because the callback was a local variable, this module used to be a real
pain to debug. I'm surprised I haven't sent more than two messages to
User talk:Undefined!!
talkback: add a simple opt-out functionality

This draws on an idea Amalthea had a while back.
talkback: fixes