contractcourt: add Launch method to anchor/breach resolver

We will use this and its following commits to break the original
`Resolve` methods into two parts - the first part is moved to a new
method `Launch`, which handles sending a sweep request to the sweeper.
The second part remains in `Resolve`, which is mainly waiting for a
spending tx.

Breach resolver currently doesn't do anything in its `Launch` since the
sweeping of justice outputs are not handled by the sweeper yet.

contractcourt/breach_resolver.go

@@ -47,6 +47,8 @@ func (b *breachResolver) ResolverKey() []byte {
 // Resolve queries the BreachArbitrator to see if the justice transaction has
 // been broadcast.
 //
+// NOTE: Part of the ContractResolver interface.
+//
 // TODO(yy): let sweeper handle the breach inputs.
 func (b *breachResolver) Resolve() (ContractResolver, error) {
 	if !b.subscribed {
@@ -83,6 +85,7 @@ func (b *breachResolver) Resolve() (ContractResolver, error) {
 
 // Stop signals the breachResolver to stop.
 func (b *breachResolver) Stop() {
+	b.log.Debugf("stopping...")
 	close(b.quit)
 }
 
@@ -123,3 +126,21 @@ func newBreachResolverFromReader(r io.Reader, resCfg ResolverConfig) (
 // A compile time assertion to ensure breachResolver meets the ContractResolver
 // interface.
 var _ ContractResolver = (*breachResolver)(nil)
+
+// Launch offers the breach outputs to the sweeper - currently it's a NOOP as
+// the outputs here are not offered to the sweeper.
+//
+// NOTE: Part of the ContractResolver interface.
+//
+// TODO(yy): implement it once the outputs are offered to the sweeper.
+func (b *breachResolver) Launch() error {
+	if b.launched {
+		b.log.Tracef("already launched")
+		return nil
+	}
+
+	b.log.Debugf("launching resolver...")
+	b.launched = true
+
+	return nil
+}