✨ Implement port connection dialog

Implements:
- Viewing connections (routes)
- Creating and deleting connections
- Changing volume of connectons
- Muting / unmuting connections

lib/mixing_tab.dart

@@ -27,6 +27,7 @@ class _MixingTabState extends State<MixingTab> {
                 port: p,
                 sendAction: widget.sendAction,
                 isOutput: isOutput,
+                mixerState: widget.mixerState,
               ))
           .toList(),
     );