Add screen cast recording functionality

This adds screencast recording to the luna-next compositor. It's completely based on work done by people from the Nemo Mobile project. All code parts taken from others are marked as so.

Recording can be started with

$ luna-recorder -f /tmp/screencast.dat

Stop it with CTRL+C

Then transfer the file to your local Linux PC and convert the file with

$ mencoder -demuxer rawvideo -rawvideo fps=15:w=768:h=1280:format=rgba -ovc x264 -o screencaast.mp4 screencast.dat

To record a screenshot

$ luna-recorder -f /tmp/screenshot.768x1280.rgba -n 1

and

$ convert -size 768x1280 -depth 8 screenshot.768x1280.rgba screenshot.png