[Tizen] Enable context menu settings.

In Tizen specific section 0230: Tizen Settings, it's said: the context menu should
be displayed when the user long-presses, for example, an image, text, or
link. This patch will implement this feature. The related feature is XWALK-1491
Same code could be invoked from 'Application::OnRuntimeAdded', right? I think now that Runtime even should not know about ui_delegate_, and RuntimeDelegae should rather be RuntimeUIManager (or RuntimeUIStrategy)