This change extends set of Avahi advertised printers which
works with Gtk's CUPS print backend.
It creates a temporary queue (local printer) for each
Avahi printer in CUPS instead of accessing them directly
(via CUPS library).
This makes some printers work which did not work before and
also gives users more options to change in the print dialog.
This also changes naming of printers to be in accordance with CUPS.
It uses '_' instead of '-' and has hostname appended for CUPS remote
printers.
