contractcourt: add new checkLocalChainActions method use in main state step

In this commit, we add a new `checkLocalChainActions` method. This
method differs from the existing `checkChainActions` method in that it's
only concerned with actions we should take on chain for our local state
based on the local _and_ remote state. This change ensures that we'll
now to go to chain order to cancel an HTLC that was on the remote
party's commitment transaction, but not our own.

contractcourt/chain_watcher.go

@@ -54,7 +54,7 @@ type RemoteUnilateralCloseInfo struct {
 	*lnwallet.UnilateralCloseSummary
 
 	// CommitSet is the set of known valid commitments at the time the
-	// remote party's commitemnt hit the chain.
+	// remote party's commitment hit the chain.
 	CommitSet CommitSet
 }