Adds mapView:didCancelDraggingMarker: delegate method

If drag ends but marker was not dragged, send a cancel message rather
than a drag ended message.
Add properties to GMDraggableMarkerManager to control marker animations

- Adds property markerAnimateUpDuration
- Adds property markerAnimateDownDuration
- Adds property markerAnimateUpDistance
- Adds property markerAnimateDownDistance