New recipe for displaying camera output via HDMI

[jywarren]

This should be a pretty easy one!

http://raspberrypi.stackexchange.com/questions/7609/ddg#7612

raspivid -fps 20 -t 99999999 -o - | mplayer -fps 20 -cache 1024 -

However, I'm not sure if this can be run at the same time as the built-in pi cam software, which is also accessing the camera. We may need to have a toggle to switch that off and this on.