sound: Add volume levels window

Merged Marco Melorio requested to merge melix99/gnome-control-center:volume-levels-window into main

This MR moves the stream list box to a separate window and it also moves the output volume slider in the "Output" section.

This also include a re-implementation of how the stream rows are created. It now uses a GListStore (with a filter and a sorter) to store all the GvcMixerStreams and that is bound to the GtkListBox via bind_model. This is needed to be able to store all the stream objects before the streams window is even created.

Fixes #501 (closed) and #1303 (closed).




Edited by Marco Melorio

Merge request reports