add volume widget

include/widgets/volumeWidget.hpp

@@ -0,0 +1,24 @@
+#pragma once
+
+#include <gtkmm.h>
+#include <string>
+#include <sigc++/sigc++.h>
+
+class VolumeWidget : public Gtk::Box
+{
+  public:
+    VolumeWidget();
+    virtual ~VolumeWidget();
+
+    // Refresh displayed volume from the system
+    void update();
+
+  protected:
+    // timeout handler for periodic polling; return true to keep polling
+    bool on_timeout();
+
+  private:
+    Gtk::Label m_label;
+    Glib::RefPtr<Gtk::GestureClick> m_click;
+    sigc::connection m_timeoutConn;
+};