Hook up the PS2MouseDevice to the AbstractScreen+WindowManager.

Render the mouse cursor by xor'ing the pixels. I don't know anything about
hardware cursors yet and this way we don't need to recompose the window
hierarchy every time you move the mouse. :^)

Widgets/EventLoop.cpp

@@ -53,7 +53,7 @@ int EventLoop::exec()
 
 void EventLoop::postEvent(Object* receiver, OwnPtr<Event>&& event)
 {
-    printf("EventLoop::postEvent: {%u} << receiver=%p, event=%p\n", m_queuedEvents.size(), receiver, event.ptr());
+    //printf("EventLoop::postEvent: {%u} << receiver=%p, event=%p\n", m_queuedEvents.size(), receiver, event.ptr());
     m_queuedEvents.append({ receiver, move(event) });
 }