ROS topic for visualising the detected faces

Hi there,

I just added code for publishing another ROS-topic (/face_detection/faces_video) which displays the detected faces just like in the opencv highgui window.

If this change is interesting for you guys, I'd be glad to share. 

Sadly, I changed a lot of lines just for indentation fixing. It looked terribly broken in my editor. If required, I could do another pull request where I don't touch the indentation.