Refactor:
- TextureData to handle Pixmap and Custom TextureType
- TextureData consumeCompressedData to consumeCustomData
- GLTexture function to uploadImageData to custom mipmap level

Added:
-MipMapTextureData which handles multiple TextureData to be uploaded to single mipmpa levels
MipMapTextureData fixes
Changes updated
Merge pull request #1664 from lordjone/texturedata

TextureData refactoring and mipmaps