Add htlctimeout reason to closure reasons

[TheBlueMatt]

In the issue I hit with #2282 the monitor closed the channel and this resulted in a CommitmentConfirmed shutdown reason, which is nonsense, I force-closed!

[TheBlueMatt]

This is kinda important cause the API is braindead, but given how little time is left for 116 and how much work is left for it, this doesn't need to go now.

[TheBlueMatt]

Ugh we really do need this but.... time.