Added helper tool to record image topic to a video

I was missing such a simple tool, useful to create videos for realistic unit-testing (ie, videos as acquired by the robot). The only other documented way relies on recording with `rosbag`, extracting the images and then re-encoding with `ffmpeg` for instance. It is quite cumbersome, and it is not obvious how to set the capture framerate. 

Compilation tested on Groovy only.

It relies on the standard OpenCV VideoWriter class.

It is configured to encode the video as MJPG in an AVI container (should
ensure good support accross platform. AVI is mandated by OpenCV).

The video size is acquired from the topic, but the frame-rate has to be
manually set with the node parameter 'fps' (defaults to 15 fps).