Change to a free software license

[M4xi1m3]

As discussed on Discord, I don't think that repo has to be placed under CC-BY-SA-NC. Maybe we should consider putting it under a free software license (MIT? GPL?)

Getting authorization from the contributors shouldn't be that hard.

Since that repo contains stuff from epsilon, I'd consider doing like we did for the website (free software license for the whole thing, CC-BY-SA-NC for icons/epsilon_light (or even remove those, as the theme engine takes icons from the sources if not available in the theme)).