Messages: don't fail imediately if peer is not online

If peer is not online when trying to send a message, retry when the peer goes online, up to a few weeks.

Allow users to cancel a pending sending message.

changed title from Dont fail immediatly if peer is not online to Messages: don't fail imediately if peer is not online

added SprintIn progress label

changed milestone to %Iteration 3

added SprintTo review label and removed SprintIn progress label

added SprintDone label and removed SprintTo review label

closed