Cleaved off CGTextureMapping for integration w/ the main project

• Moved all texture mapping-related functions, utils, and data structures (everything used under the `createDestImageData()` function) into new `CGTextureMapping.h`/`.c` files.
	» Plain-C, usable anywhere!
	» Replace `BOOL` usage with stdbool’s `bool` and `NSCAssert()` with assert.h’s `assert()`.
	» `MIN()` and `MAX()` macros are also part of NSObjCRuntime.h, so created new `clampi()` and `withinin()` util functions.
• Moved GLKit extension functions into new `GLKMathExtensions.h`/`.inl` files.
	◦ Had to disable CLANG_ENABLE_MODULES in project in order allow inclusion of just `GLKit/GLKMath.h` (which is plain-C-friendly), instead of includin all of `GLKit/GLKit.h` (which only works with Obj-C).
• Minor: Removed the inclusion of UIKit and Foundation from the `.pch`.  Not really necessary.