[phil65]

Ported some first stuff from my SkinConverter tool.

Skin sanity checking:
- Check Variables (find unused variables and undefined var references)
- Check Includes (same)
- Check for invalid xml nodes

EDIT: at the moment it is hardcoded to use the "1080i" folder, will fix that.

EDIT2: different xml folders should work now, but includes with condition attributes lead to false positives atm. will get fixed.