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`.

rpcserver.go

@@ -729,7 +729,7 @@ func (r *rpcServer) addDeps(s *server, macService *macaroons.Service,
 			return info.NodeKey1Bytes, info.NodeKey2Bytes, nil
 		},
 		FindRoute:              s.chanRouter.FindRoute,
-		MissionControl:         s.missionControl,
+		MissionControl:         s.missionControl.GetDefaultStore(),
 		ActiveNetParams:        r.cfg.ActiveNetParams.Params,
 		Tower:                  s.controlTower,
 		MaxTotalTimelock:       r.cfg.MaxOutgoingCltvExpiry,
@@ -6071,7 +6071,8 @@ func (r *rpcServer) AddInvoice(ctx context.Context,
 
 			return r.server.chanRouter.FindBlindedPaths(
 				r.selfNode, amt,
-				r.server.missionControl.GetProbability,
+				r.server.missionControl.GetDefaultStore().
+					GetProbability,
 				blindingRestrictions,
 			)
 		},