DolphinQt: Properly handle quit events.

* Confirm stopping emulation when the window is closing, not just the "Stop" button
 * Don't resume if we were already paused when we got the quit event
 * Shutdown the core at the end of main() so we don't crash on exit
 * Miscellaneous other logic cleanups related to this

Source/Core/DolphinQt/Main.cpp

@@ -60,6 +60,7 @@ int main(int argc, char* argv[])
 
 	int retcode = app.exec();
 	delete g_main_window;
+	Core::Shutdown();
 	UICommon::Shutdown();
 	return retcode;
 }