xfce4-mixer -> gtk-mixer

[Rozhuk Ivan]

Hi!

I am was very dissapointed that xfce4-mixer is deprecated, so I am rewrite it to
new app - GTK-Mixer.

GUI mostly same, but many features now work:
- show all sound cards
- handle sound card connect/disconnect
- handle default device change
- allow switch default sound device
- tray icon (like audio/volumeicon / audio/gvolwheel)

It does not require nothing but gtk3.
If some one want - feel free to write ALSA/sndio/... sound backend plugins.


https://github.com/rozhuk-im/gtk-mixer
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=253150