[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
let's do the following:
1) Add new interface RuntimeUIDelegate (whithin the same folder where Runtime is)
2) Add virtual RuntimeUIDelegate::Show(Runtime*)  // the current Runtime::AttachWindow code should go there.
3) Add Runtime::SetUIDelegate(RuntimeUIDelegate*);
4) add Runtime::set_window(NativeAppWindow* window ) // to be called from RuntimeUIDelegate impl