app: set subtitle using VTE name
Currently, subtitle indicate the monitor number, ex: "Fedora (1)".
Custom subtitle use %d to place the monitor number.
Let's make this placeholder more generic to place the name of the
console, ex: "Fedora (Serial)".
Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Acked-by: Victor Toso <victortoso@redhat.com>