Restore application on AE_RESUME.

Bug: XWALK-2578

Signed-off-by: Nicolas Guyomard <nicolas.guyomard@open.eurogiciel.org>
no objections, I just feel a bit uncomfortable seeing "NativeAppWindow::Restore()"  method being invoked from "ApplicationTizen::Show" (NativeAppWindow::Show() would look more natural here).