LibCore+LibGUI: Remove GEventLoop and use CEventLoop everywhere

GEventLoop was just a dummy subclass of CEventLoop anyway. The only
thing it actually did was make sure a GWindowServerConnectionw was
instantiated. We now take care of that in GApplication instead.

CEventLoop is now non-virtual and a little less confusing. :^)

Libraries/LibCore/CEventLoop.cpp

@@ -181,6 +181,7 @@ CEventLoop& CEventLoop::current()
 
 void CEventLoop::quit(int code)
 {
+    dbg() << "CEventLoop::quit(" << code << ")";
     m_exit_requested = true;
     m_exit_code = code;
 }