Catkinized packages, added python script and launch file to continouosly compress last 20s of openni depth topic

This adds nodes for saving the openni_launch outputs to png file (will change to tiff), 3x8 bit in rgb case and 1x16 in depth case. There is also one python node for compressing the depth images from the last 20s (will change to longer intervals) into a lossless ffv1 movie format using the libav convenience wrapper, avconv. The infrastructure should also be the same for the rgb video stream, but probably using the lossless version of x264. To be able to run the code, you need to have libav v. 9 installed. Since v. 8 (I think, or 7) is the default on ubuntu 12.04 I suggest to compile this from source as instructed in the wiki. The code assumes you run the configure script with prefix ~/libav. To launch the compression, run roslaunch libav_compressor video_saver.launch. The openni_launch needs to run before that. The images will be saved in openni_saver/images (they will only be there before being compressed) and the final videos in libav_compressor/videos. I will update the wiki shortly with the new instructions.