[refactor] introduce a new Corethread Event consume method

[lidaobing]

Currently, the only way to consume corethread event is registering callback on CoreThread.signalEvent. Example:

iptux/examples/count-bot/main.cpp

Lines 47 to 48 in cf49769

	thread->signalEvent.connect(
	[=](shared_ptr<const Event> event) { processEvent(thread, event); });

But it's not suitable for UI(which has its own mainloop). so we need to use an adaptor to queue it in the mainloop, which make things too complex. Example:

iptux/src/iptux/EventAdaptor.cpp

Lines 26 to 29 in cf49769

	void EventAdaptor::processEvent(std::shared_ptr<const Event> event) {
	EventData* callback = new EventData(this, event);
	g_idle_add(processEventCallback, callback);
	}

we need to add some methods to corethread, to make the consumer easier to write.

CoreThread.CountEvent
CoreThread.HasEvent
CoreThread.PopEvent