Made the strandsbag play.launch and record.launch, which are supposed to be used as rosbag

This commit makes the use of the compression more convenient as it enables it to use with rosbag. You can now record a rosbag with roslaunch strandsbag record.launch f:=(FILE) and view it with roslaunch strandsbag play.launch f:=(FILE). The nodes make sure that the image streams are published at the same time that they were recorded originally by looking at the saved timestamps of the video frames/images and synch them with the rosbag simulated time.

At the moment you need to decompress the videos with roslaunch libavcompressor video_loader.launch before you can use play.launch. This is to be automated so that decompression is automatically run as we need more recent frames and the old frames are deleted.

The api of strandsbag should also be made to more or less mirror that of rosbag.

Also, I will sit down tomorrow and try to comment as much of the code as possible, and do some documentation.