webadmin: Display VncKeyboardLayout only for VNC display

Added missing ModeSwitchingVisibilityRenderer to
vncKeyboardLayoutEditor.

Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1057591
Change-Id: I39b48037d5ea4ef2a909cd7ff0e79d1a7690b5e1
Signed-off-by: Martin Betak <mbetak@redhat.com>