Bug fixes/refactoring in core-util-examples

-CoreExample now extends RenderLoopCallback, so all CoreExample classes now ONLY implement CoreExample.
-ExampleMain now prints class name for each example instead of saying SuperSimpleExampleMain for everything (oops) :/
-CoreSetupLwjgl no longer requests OpenGL 3.2 on init (idk why it was doing that?) -- it now uses the default ContextAttribs constructor which grabs the highest available OpenGL core profile
-Fixed CoreSetupJogl not resetting frame count after updating FPS string
-Fixed CoreSetupJogl enableVSync method; upon calling the method, a flag is set to update the vsync setting in the GL context upon the next call to 'display' in GLEventReceiver - this prevents enableVSync from throwing a GLException if the caller is not the thread holding ownership of teh GL context.
-Added SimpleFPSBenchmark class (at least temporarily) to run simple performance tests on the two backends.