DECORATE parser work.

Parser can now handle old-style definitions and damagetypes definitions.
Parser can now handle native actors, so it can parse zdoom.pk3.
Parser now handles game filters.
Added support for actor scale, including for 3D rendering.
Added a missing ZDoom thing.
Added some multiplayer things to ZDoom config.
Miscellaneous fixes to recent changes.
Game filters.
Urban Brawl (+ extension) config.
Don't repeat PNG optimization error messageboxes.

The warning is now done beforehand when selecting multiple entries.
Merge pull request #60 from Gaerzi/master

Sync with my fork.