[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
5) Add ApplicationPageUIDelegate: public RuntimeUIDelegate (within the same folder where Application class is)
6) Application should own ApplicationPageUIDelegate and set it to the Runtimes when those are created
7) ApplicationPageUIDelegate constructor should accept NativeAppWindow::CreateParams (from Application).
8) from Runtime::WebContentsCreated call
if (ui_delegate_)
    ui_delegate_->show(new_runtime);

..........
9) Runtime::Attach.. methods go away