Support for passing an existing tcpVideoStream

Since the AR Drone supports only a single connection to the video
stream, it is sometimes required to re-use the same stream across an
application.

If no tcpvideostream is passed, the behavior is the same as before, nothing as changed. If a stream is passed, then it is re-used.

Related to this issue in node-ar-drone: https://github.com/felixge/node-ar-drone/issues/43