WIP:Blentran

Blendmode and transparency support for MORE STUFF, including FOFs and linedefs (ported from Kart internal).

Introduces REAL BEHIND-THE-SCENES GAMMA CORRECTION to the palette for effects' sake!

Currently requires (most to least priority):

• OPENGL BUG - ALL transparent mobjects broked - this worked fine in Kart, wonder what messed it up
• OPENGL BUG - Transparent planes with blendmodes broked - this worked fine in Kart, wonder what messed it up
• add a UDMF field that allows linedefs to have set blend types, instead of a hacky linedef number system
• Reimplement the blendmode field for mobjects instead of using space blocked out in renderflags (at nev3r's request)
• OPENGL PARITY - All blendmodes in OpenGL need to be modified to use gamma-corrected colourspace
• (dreamin') A complete rewrite of the V_CubeApply function to work in gamma-corrected colourspace

Effectively equivalent with master, but just in case please don't use this branch for netgames. A Windows executable can be provided on request.