More improvements to Oil Gen

Oil Lakes can no longer only spawn in sand. Added IMC calls for Lakes
and excluded Biomes.
"oil-lake-biome" and "oil-gen-exclude", both take the BiomeID as an
argument.

Increased specular highlights on Oil texture, you shouldn't have to jump
in the pool to tell the difference between lighting glitches and oil
anymore.

Oil Lakes now have 50% chance of being 2 blocks deep. Improved gen to
prevent floating trees, etc.

Oil Wells should no longer gen in mod added trees.