Added debug code, the compression is working completely lossless at 10 times compression of depth

This adds the test_quality c++ node, which takes the input uncompressed images and output, decompressed images and compare them graphically. The node is launched with roslaunch libav_compressor test_quality.launch. To be able to run this code you need to uncomment the debug lines in batch_compressor.py before running video_saver.launch and video_loader.launch. But after that you can just run test_quality.launch directly. I will change this debug option to be a parameter to the video_saver.