Support for remote control buttons (#300)

* refactor beacon function inside IR sensor

* towards sim support

* channel labels

* reverting to singletons

* hiding unused apis

* lazy allocation of button instances

* tracking button state

* hook up the state

sim/visuals/board.ts

@@ -234,6 +234,8 @@ namespace pxsim.visuals {
                     const state = ev3board().getInputNodes()[0] as InfraredSensorNode;
                     if (state.getMode() == InfraredSensorMode.Proximity)
                         view = new ProximitySliderControl(this.element, this.defs, state, port);
+                    else if (state.getMode() == InfraredSensorMode.RemoteControl)
+                        view = new RemoteBeaconButtonsControl(this.element, this.defs, state, port);
                     break;
                 }
                 case NodeType.GyroSensor: {