Add portable home directory support

Add a settings directory in directory with binary for portable usage on USB flash drives or whatever.

(Ported from Turtle Arena, without the stupid requiring a file named settings/portable containing "yes".)
Merge remote-tracking branch 'spearmint/master'

Conflicts:
	code/qcommon/files.c
Remove FS_BaseFileExists

It's unused and I don't remember why I added it.
Allow custom music on pure servers

Added from Turtle Arena.
Merge remote-tracking branch 'spearmint/master'

Conflicts:
	code/qcommon/files.c
Merge remote-tracking branch 'ebx/master'