Relicense assets to be DFSG compliant

[qwertychouskie]

Right now the assets are mostly "free-to-listen-to" or CC-BY-SA-NC. Assets should be relicensed to be DFSG (Debian Free Software Guidelines) compatible (preferably CC-BY-SA 4.0 International), or otherwise replaced.

Why is this needed?

Having assets with a non-DFSG-compatible license (or no license) means that Cubosphere can't be distributed on many platforms without potential issues; also, to have Cubosphere be packaged in Linux distributions requires properly-licensed assets.

Music

• [ ] Aquatopia.mp3
• [ ] Arabic Desert.mp3
• [ ] Arctican.mp3
• [ ] At the Speed of Light.mp3
• [ ] Cave Ambient 2.mp3
• [ ] Cavern of Memory.mp3
• [ ] Core of the Storm.mp3 | Sent email
• [ ] Corridors.mp3
• [ ] Data Empire.mp3
• [ ] Deep Man.mp3 (currently CC-BY-SA-NC 3.0)
• [ ] Endless Day of Grass Field.mp3 (currently CC-BY-SA-NC 3.0)
• [ ] Escape from the Citadel.mp3
• [ ] Everything is Floating Upward.mp3 (currently CC-BY-SA-NC 3.0)
• [ ] Heretical Mysticism.mp3
• [ ] Hyperspace.mp3
• [ ] Journey to the East.mp3
• [ ] Jungle Bed.mp3
• [ ] Melodies de Mars.mp3 (currently CC-BY-SA-NC 3.0)
• [ ] Mindmangler.mp3 (currently CC-BY-SA-NC 3.0)
• [ ] Never Stop.mp3 | In progress, https://www.newgrounds.com/audio/listen/337730
• [ ] Orchestral Theme.mp3
• [ ] Perfect Morning.mp3 (currently CC-BY-SA-NC 3.0)
• [ ] Persian Invasion.mp3
• [ ] Rose At Meridiem.mp3
• [ ] Rose At Twilight.mp3
• [ ] Ruin.mp3
• [ ] Running through Greece.mp3
• [ ] Space_Forest.mp3
• [ ] Stellar.mp3
• [ ] Sun and Rainfall.mp3
• [ ] Thatianne and the Sylph.mp3
• [ ] The Sun Will Come.mp3
• [ ] Triumphant Returns.mp3
• [ ] Ziggurat.mp3 (This is a remix of a MOD, may make things more complicated) | In progress, https://www.newgrounds.com/audio/listen/167762

Textures

• [ ] TODO: Fill in list

SFX

• [ ] TODO: Fill in list