drop the current transparency code

we will leverage the alpha channel when the need will
arise again.
drop the TexEnv rasterizer

drop as well the companion code and the remaining palette generation
code.
trim no longer used fields

adapt the client code too.
renamed for consistency (?)
switch to EON_Color in EON_Mat.
minor cleanup
switch to the EON_ScrPoint structure.
renamed parameter for compactness.

TriFace->Face