feat(SebmGoogleMap): support idle event

This event is fired when the map becomes idle after panning or
zooming.

Example:

```
<sebm-google-map [latitude]="lat" [longitude]="lng" (idle)="myMethod">
</sebm-google-map>
```

Closes #393
Closes #417

src/core/directives/google-map.ts

@@ -40,7 +40,7 @@ import {MarkerManager} from '../services/marker-manager';
  'backgroundColor', 'draggableCursor', 'draggingCursor', 'keyboardShortcuts', 'zoomControl',
  'styles', 'usePanning'
  ],
- outputs: ['mapClick', 'mapRightClick', 'mapDblClick', 'centerChange'],
+ outputs: ['mapClick', 'mapRightClick', 'mapDblClick', 'centerChange', 'idle'],
  host: {'[class.sebm-google-map-container]': 'true'},
  styles: [`
  .sebm-google-map-container-inner {
@@ -168,6 +168,11 @@ export class SebmGoogleMap implements OnChanges,
  */
  centerChange: EventEmitter<LatLngLiteral> = new EventEmitter<LatLngLiteral>();
 
+ /**
+ * This event is fired when the map becomes idle after panning or zooming.
+ */
+ idle: EventEmitter<void> = new EventEmitter<void>();
+
  constructor(private _elem: ElementRef, private _mapsWrapper: GoogleMapsAPIWrapper) {}
 
  /** @internal */
@@ -191,6 +196,7 @@ export class SebmGoogleMap implements OnChanges,
  this._handleMapCenterChange();
  this._handleMapZoomChange();
  this._handleMapMouseEvents();
+ this._handleIdleEvent();
  }
 
  /* @internal */
@@ -254,6 +260,11 @@ export class SebmGoogleMap implements OnChanges,
  });
  }
 
+ private _handleIdleEvent() {
+ this._mapsWrapper.subscribeToMapEvent<void>('idle').subscribe(
+ () => { this.idle.emit(void 0); });
+ }
+
  private _handleMapMouseEvents() {
  interface Emitter {
  emit(value: any): void;