Promote global functions and variables for PVR decryption to ZipUtils class.
Rename PVR decryption functions and variables to better fit in the Cocos2DX framework.
Improve log error notes.
Update TextureAtlasEncryptionTest to match revised function call in ZipUtils.
Update ccSetPvrEncryptionKeyPart documentation to clarify that encryption is never 100% secure.
Merge branch 'TexturePacker-SpriteSheetProtection' into FPG_Development