Add libre music replacements (no NC clause)

Created by: akien-mga

Part of #1 (closed).

@Cirrus-Minor What do you think of the tracks I found? I couldn't really find a gameover track similar to the previous one, nor a groovy/jazzy track for the main menu, but there is still room for improvement later on, it's just a quick replacement after some time of browsing OGA and other sources of CC BY(-SA) music.