This ports the application to libadwaita, enabling us to use the libadwaita stylesheet and
widgets to better implement the Gnome Human Interface Guidelines.
Glib MainContext is now aquired manually because a change in gtk-rs would lead to
a panic when attaching the receiver otherwise, because gtk::init() doesn't
"leak" the default main context anymore.
The pipewire loop now runs without interruption in a second thread and communicates with
the GTK thread via a channel in each direction, instead of checking for events once a second and using callbacks.
This allows changes to appear instantly in the view, instead of having to wait.
struct PipewireConnection is now decoupled from any other components, another component (the controller)
can receive updates by registering a callback.
struct PipewireState has been refactored to a struct Controller.
It still keeps state and manages the view, but now also actively requests updates from the pipewire connection via callback.
This updates all crates to their newest release.
For pipewire-rs, this includes bumping the version to 0.3, which means this comment has to fix a few breaking changes, but nothing big.
0.3 also lets us create and delete remote objects, which will be needed for link creation and deletion.
