Reorganise GG2 directory structure

[hikari-no-yume]

Gets rid of that Source anachronism and renames gg2 to Gang Garrison 2.

[hikari-no-yume]

This doesn't do anything bad on Windows, though it doesn't do anything either.

[Medo42]

I don't really see the point unless it's to confuse people (especially Windows devs).

[hikari-no-yume]

Well... it means the music works when run from Source. On non-Windows systems, anyway :P

[Medo42]

Maybe we should re-organize the source tree a bit then... e.g. move Music into Source directly, or move the gmk build scripts to the base dir and let them drop the .gmk there. Something that also helps the Windows users.

[hikari-no-yume]

We could just make it (mostly) match the structure of the zip file, except having gg2.gmk in the root, instead of at Source/Gang Garrison 2.gmk

[hikari-no-yume]

OK I completely changed this pull request. Now it reorganises GG2's dir structure rather than symlinking Music.

[hikari-no-yume]

this PR is bad and I feel bad