Added timestamps to be able to recreate the stream later together with a rosbag

This names the files (also intermediate video) to the ros timestamps of the messages. During video storage, timestamps are stored in separate text files. The association of depth and color should be slightly better now. The subscribed image topics should probably be some other ones. Also updated the quality test of the depth video to be able to run with the new names. Right now, the debug lines in batch_compressor.py are uncommented so you are still storing the images on your computer when running video_saver.launch. Next step is to see if we can use the time topic from a rosbag with simulated time to publish the topics at the same time as we received them together with the rosbag topics.