Improved ZDoom support

- More text lumps recognized
- List of keywords for various ZDoom languages updated
- DECORATE parser is now able to find sprites from states in the same
way as Doom Builder 2
- Sprites from states can be found even if the lump does double-duty
(e.g. BOS2A1C1 from doom2.wad will be found correctly for the BOS2 A
state)
Merge branch 'master' of https://github.com/Gaerzi/SLADE