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/missioncontrol_state.go

@@ -37,7 +37,8 @@ func newMissionControlState(
 	}
 }
 
-// getLastPairResult returns the current state for connections to the given node.
+// getLastPairResult returns the current state for connections to the given
+// node.
 func (m *missionControlState) getLastPairResult(node route.Vertex) (NodeResults,
 	bool) {
 
@@ -45,8 +46,8 @@ func (m *missionControlState) getLastPairResult(node route.Vertex) (NodeResults,
 	return result, ok
 }
 
-// ResetHistory resets the history of MissionControl returning it to a state as
-// if no payment attempts have been made.
+// ResetHistory resets the history of missionControlState returning it to a
+// state as if no payment attempts have been made.
 func (m *missionControlState) resetHistory() {
 	m.lastPairResult = make(map[route.Vertex]NodeResults)
 	m.lastSecondChance = make(map[DirectedNodePair]time.Time)