Camera start, ongoing, and end events notifications

[zugaldia]

The latest Google Maps has added camera change listeners for camera start, ongoing, and end events notifications. The interfaces are OnCameraMoveStartedListener, OnCameraMoveListener, OnCameraMoveCanceledListener, OnCameraIdleListener. This is how it's described in the announcement:

As one of our top requests, developers have been asking for a better way to track camera movements and the ability to see why the camera is moving, whether caused by user gestures, built-in API animations or developer controlled movements [Issue 4636]. Our new camera change listeners support you in doing this. Your app can now receive notifications for camera start, ongoing, and end events.

I hear these are useful and we should consider supporting them as well for API parity.

/cc: @cammace @tobrun

[tobrun]

This landed on the release branch. Closing.