routing: separate MissionControl from MissionControlManager

This commit renames the previous MissionControl to MissionController and
the previous MissionController interface to MissionControlQuerier. This
is done because soon the (new) MissionController will back multiple
namespaced MissionControl instances.  For now, it just houses a single
MissionControl in the default namespace.

This commit also replaces the MissionControl's `now` function with a
`clock.Clock`.

routing/payment_session.go

@@ -159,7 +159,7 @@ type PaymentSession interface {
 
 // paymentSession is used during an HTLC routings session to prune the local
 // chain view in response to failures, and also report those failures back to
-// MissionControl. The snapshot copied for this session will only ever grow,
+// MissionController. The snapshot copied for this session will only ever grow,
 // and will now be pruned after a decay like the main view within mission
 // control. We do this as we want to avoid the case where we continually try a
 // bad edge or route multiple times in a session. This can lead to an infinite
@@ -184,7 +184,7 @@ type paymentSession struct {
 	// trade-off in path finding between fees and probability.
 	pathFindingConfig PathFindingConfig
 
-	missionControl MissionController
+	missionControl MissionControlQuerier
 
 	// minShardAmt is the amount beyond which we won't try to further split
 	// the payment if no route is found. If the maximum number of htlcs
@@ -199,7 +199,8 @@ type paymentSession struct {
 // newPaymentSession instantiates a new payment session.
 func newPaymentSession(p *LightningPayment, selfNode route.Vertex,
 	getBandwidthHints func(Graph) (bandwidthHints, error),
-	graphSessFactory GraphSessionFactory, missionControl MissionController,
+	graphSessFactory GraphSessionFactory,
+	missionControl MissionControlQuerier,
 	pathFindingConfig PathFindingConfig) (*paymentSession, error) {
 
 	edges, err := RouteHintsToEdges(p.RouteHints, p.Target)
@@ -266,7 +267,7 @@ func (p *paymentSession) RequestRoute(maxAmt, feeLimit lnwire.MilliSatoshi,
 
 	// Taking into account this prune view, we'll attempt to locate a path
 	// to our destination, respecting the recommendations from
-	// MissionControl.
+	// MissionController.
 	restrictions := &RestrictParams{
 		ProbabilitySource:     p.missionControl.GetProbability,
 		FeeLimit:              feeLimit,