Provide integrated music cover thumbnail

The objective is to provide a thumbnail for music files independently from the music program. As a matter of fact, video and images thumbnails are available thanks to capture, but music files/directory is displayed poorly. This is a important lack for modern OS dealing with lots of media (and music is one of the major use for personal computer today). Thus, this feature includes the ability to fetch the cover when ripping a CD, to save the cover file accordingly, and to use it for display in every programs, in particular in nautilus. Obviously, this feature cannot only rely on ripping program, but needs to retrieve covers from existing collection. Moreover, this will have surely lots of impacts/relation with existing music programs