Add a VirtViewerDisplayVte display kind
    
    This is not a graphical display, so the application will have to deal
    with it with care.
    
    You may argue that we need a large refactoring to introduce a more
    generic "console" object, that could be either graphical or textual.
    For now, this does work well enough for me.
    
    Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
    Acked-by: Victor Toso <victortoso@redhat.com>