- (linux) XDG filesystem support

BIG NOTE TO LINUX USERS
All user data has been moved according to XDG specs:
- Game data (H3 files and mods) and saves: from ~/.vcmi to ~/.local/
- Temporary files, including logs: from ~/.vcmi to ~/.cache/vcmi
- Config files: from ~/.vcmi/config to ~/.config/vcmi

For compatibility VCMI will read game data from ~/.vcmi as well but this
is temporary behavior and will be removed


git-svn-id: http://svn.code.sf.net/p/vcmi/code/trunk/@3798 4dfc6b2a-8b31-0410-aa91-d6c70e3ac834