Reorg: Moved int/float math functions into MathExtensions

• Moved int/float math util functions and constants from CGTextureMapping.cpp’s “Util Functions” section into new `MathExtensions.h`/`.inl` files.
	• `MathExtensions.inl` and `GLKMathExtensions.inl` both set in project to type “C Header”.
	• `barycentricCoords2()` moved down in the file to be next to surfaceSTToTexelUV_barycentricTri().
• Also, added `@source` doc-comment to the modulo_i() function referencing the StackOverflow answer I got it from.