Cancel Swap API

I realize cancelling a swap mid-swap would be kind of bad, but there are situations where it appears to me like peerswap has mentioned in the logs that something has timed out, but it doesnt move the swap state to a cancelled state.

Currently I have a stuck swap in this state: `State_SwapOutSender_AwaitTxBroadcastedMessage`

In general, would be good to have a way to explicity say "I know what I am doing, cancel the swap", because currently I've tried, disconnecting the peer, and restarting the daemon, but the swap wont go away.