wip: refactor pt.33: 33e; midi player traits

crates/tek_api/src/todo_api_mixer.rs

@@ -0,0 +1,11 @@
+use crate::*;
+
+#[derive(Debug)]
+pub struct Mixer {
+    /// JACK client handle (needs to not be dropped for standalone mode to work).
+    pub jack:            Arc<RwLock<JackClient>>,
+    pub name:            String,
+    pub tracks:          Vec<MixerTrack>,
+    pub selected_track:  usize,
+    pub selected_column: usize,
+}