figments: command: rewrite command api to use Task instances instead of static functions

src/Sequencer.h

@@ -28,4 +28,7 @@ public:
 private:
     int m_idx;
     std::vector<Scene> m_scenes;
+
+    void doScene(Args& args, Print& out);
+    void doScenes(Args& args, Print& out);
 };