Show just-completed NPC if repeating a task.

Put old NPC on correct side depending on side of
next NPC.

[#70037500]
Show "Thanks again!" message when old task is completed for second time.

Correctly show fail message when old task fails.

[#69270664]
Ensure final speech bubble is hidden on task replay

Previously if you replayed a task while final speech was
showing, the final bubble would remain visible.

[#69270664]