Add TrueColor option to Android/iOs

Without using RGBA8888 is ulgy but hopefully disable it can get better performance and less memory usage in Android/iOS by rendering color depthas 16bit only .  

Quoted from Apple 
"If your application cannot use compressed textures, consider using a lower precision pixel format. A texture in RGB565, RGBA5551, or RGBA4444 format uses half the memory of a texture in RGBA8888 format. Use RGBA8888 only when your application needs that level of quality."