Store GameResources in ResourceLibrary instead of all Resources in Sandbox.Engine so resources get released properly on game shutdown Every native resource (model, material, textures...) was getting held indefinitely even after game shutdown, this commit solves that by: * ResourceLibrary will only hold strong references to GameResource, native resources will only have a weak reference internally this way they get unloaded properly. * Sandbox.Tools gets it's own ResourceLibrary, doesn't piggy back from GameHost.Menu anymore * Get rid of GameHost from Resources