Implement M2 vertex shaders matching Wrath of the Lich King

[fallenoak]

Several M2 vertex shaders are present in Wrath of the Lich King, and need to be implemented in Wowser to correctly render M2s.

Work on this issue depends on implementation of #132 and should be done in conjunction with #137.

Progress

• Diffuse_T1
• Diffuse_Env
• Diffuse_T1_T2
• Diffuse_T1_Env
• Diffuse_Env_Env

Notes

• The shader names are in the syntax of <coordinate-1>_<coordinate-2>
• A value of T1 indicates coordinate-# should come from the first UV coordinate defined in the vertex data present in the M2 file
• A value of T2 indicates coordinate-# should come from the second UV coordinate defined in the vertex data present in the M2 file
• A value of Env indicates coordinate-# should be calculated via spherical environment mapping (based on the camera's position relative to the vertex)