Resource gathering

We have two sources of free resources:

- [Remastered Tyrian Graphics](http://www.lostgarden.com/2007/04/free-game-graphics-tyrian-ships-and.html) available under the terms of [Lost Garden License](http://www.lostgarden.com/2007/03/lost-garden-license.html) — _note it forbids to use the content for cloning the commercial game, so I'll need to ask the author for additional permission_
- [Tyrian: Original Soundtrack](https://alexanderbrandon.bandcamp.com/album/tyrian-original-soundtrack) — license isn't mentioned anywhere, so we'll also need to clarify

Also I'm contacting original Tyrian lead developer to ask for the original resource versions (OpenTyrian also requires them, but user should download them on their own behalf).