LibCore+LibGUI+WindowServer: Make events bubble up through ancestors

With this patch, CEvents no longer stop at the target object, but will
bubble up the ancestor chain as long as CEvent::is_accepted() is false.

To the set accepted flag, call CEvent::accept().
To clear the accepted flag, call CEvent::ignore().

Events start out in the accepted state, so if you want them to bubble
up, you have to call ignore() on them.

Using this mechanism, we now ignore non-tabbing keydown events in
GWidget, causing them to bubble up through the widget's ancestors. :^)

Libraries/LibCore/CEventLoop.cpp

@@ -245,7 +245,7 @@ void CEventLoop::pump(WaitMode mode)
 #endif
             static_cast<CDeferredInvocationEvent&>(event).m_invokee(*receiver);
         } else {
-            receiver->event(event);
+            receiver->dispatch_event(event);
         }
 
         if (m_exit_requested) {