Add video playback start point when using authentication

When starting a Cast session using authentication and the authentication process is complete and ready to start playback, the callback needs to be able to take a start point in the video. This will allow videos that require authentication on the sender device to be able to set a start position.

**Note**
*This is a breaking change.* A alternative to this modification would be to add another overloaded `startCastControllerActivity` method to the `VideoCastManager` that would take a `Context`, `IMediaAuthService`, and a `startPoint`  parameter. Then pass the `startPoint` and an extra on the `Intent` to start the `VideoCastControllerActivity`. Inside the `onCreate` method of the `VideoCastControllerFragment` when it checks for a `VideoCastManager.EXTRA_HAS_AUTH` extra, it would have to also check for the `startPoint` extra and assign it to a a new member variable so that when the `onResult` callback method is called, it can send that `startPoint` to the `onReady` method.