Add ability to build GTK app AppImage (#240)

#238 Add AppImage build support

Implements

- Downgrade to libadwaita 1.3 for wider distro support
- Add build script, workflow, and docs for AppImage
- Add build docs for Debian (apt) and Void Linux
- Building AppImage in CI

burrow-gtk/src/components/switch_screen.rs

@@ -29,7 +29,7 @@ impl AsyncComponent for SwitchScreen {
     view! {
         gtk::Box {
             set_orientation: gtk::Orientation::Vertical,
-            set_valign: Align::BaselineFill,
+            set_valign: Align::Fill,
 
             gtk::Box {
                 set_orientation: gtk::Orientation::Vertical,