Added NPOT support checks to CoreUtil; fixed NPE in TextureAtlastGeneratorMain

-CoreUtil now defines isNPOTHardwareSupported() and isNPOTSupported() for checking NPOT texture support
-Changed JoglCoreUtil and LwjglCoreUtil from public visibility to default (package-only)
-Fixed TextureAtlasGeneratorMain not initializing CoreRender

NOTE: TextureAtlastGeneratorMain still does not seem to be working properly. It looks weird on JOGL, and does not work at all in LWJGL (CoreTexture2D prints a pre-mature finalization by GC warning).