feat(SebmGoogleMap): support double-click event

Now, you can subscribe to double-click events:

```
<sebm-google-map
  [latitude]="lat"
  [longitude]="lng"
  (mapDblClick)="mapClicked($event)">
</sebm-google-map>
```

The $event is a `MapMouseEvent` type that contains
the coords of the double-click.

```
import {MapMouseEvent} from 'angular2-google-maps/core';

class App {
  mapClicked(event: MapMouseEvent) {
    console.log(event.coords.lat, event.coords.lng);
  }
}
```

Author: sebholstein

docs/api/components_directives/sebmGoogleMap.md

@@ -32,10 +32,11 @@ import {SebmGoogleMap} from 'angular2-google-maps/core';
 
 ### Events
 
-| Event name    | Arguments                       | Description                                              |
-|---------------|---------------------------------|----------------------------------------------------------|
-| mapClick      | [MapMouseEvent](#MapMouseEvent) | Gets emitted when the user clicks on the map             |
-| mapRightClick | [MapMouseEvent](#MapMouseEvent) | Get emitted when the user uses a right click on the map. |
+| Event name    | Arguments                       | Description                                                                                                                         |
+|---------------|---------------------------------|-------------------------------------------------------------------------------------------------------------------------------------|
+| mapClick      | [MapMouseEvent](#MapMouseEvent) | Gets emitted when the user clicks on the map                                                                                        |
+| mapRightClick | [MapMouseEvent](#MapMouseEvent) | Gets emitted when the user uses a right click on the map.                                                                           |
+| mapDblClick   | [MapMouseEvent](#MapMouseEvent) | Gets emitted when the user double-clicks on the map.  Note that the `mapClick` event emitter will also fire, right before this one. |
 
 ### Event Interfaces
 

src/directives/google-map.ts

@@ -30,6 +30,7 @@ export class SebmGoogleMap {
 
   @Output() mapClick: EventEmitter<MapMouseEvent> = new EventEmitter<MapMouseEvent>();
   @Output() mapRightClick: EventEmitter<MapMouseEvent> = new EventEmitter<MapMouseEvent>();
+  @Output() mapDblClick: EventEmitter<MapMouseEvent> = new EventEmitter<MapMouseEvent>();
 
   constructor(elem: ElementRef, _mapsWrapper: GoogleMapsAPIWrapper, renderer: Renderer) {
     this._mapsWrapper = _mapsWrapper;
@@ -106,7 +107,8 @@ export class SebmGoogleMap {
 
     const events: Event[] = [
       {name: 'click', emitter: this.mapClick},
-      {name: 'rightclick', emitter: this.mapRightClick}
+      {name: 'rightclick', emitter: this.mapRightClick},
+      {name: 'dblclick', emitter: this.mapDblClick}
     ];
 
     events.forEach((e: Event) => {