Introduced flexible "framerate limit" setting.

Instead of an on/off "limit" switch, there are now several FPS limits to choose from: {20, 30, 40, 60, 75, 85, 120, 144}. Any modes above user's monitor refresh rate will not be shown. Value of "0" means "no limit". The setting has been renamed from "limitFramerate" to "framerateLimit", but backwards compatibility is preserved.