Should be zeroed by glib.

To set both channels to euqal value, decrease the volume to 0
and increase again.

Closes #90

Closes #91

Set the default controlled player when it starts playback instead when
it connects to MPRIS interface.

Amends 501f1a52

Closes: #46

Players are now identified by their real name. It prevents storing all
player's instances in config file. It's not backward compatible, so the
settings keys are different now.

All players disappears from menu after closing by default (possible to
change the behavior in settings dialog).

By doing all these changes, Chromium started working, too.

Closes: #26
Closes: #70
Closes: #87

Don't wait too long if player is not responding.

- some code refactor
- destroy mpris player object on player disconnection

Also destroy MPRIS object on quit

Closes: #65

Amends: e81ce6f1

It allows to use arguments, e.g. "pavucontrol -t 1"

It's not possible to make unplugged device default, so let's make the
menu item insensitive. The device exists, but it's not possible to
choose it.

Closes: #83

Useful for obs-pipewire-audio-capture when audio is captured directly
from application and it's not connected to the real device.