add group feature

include/group.hpp

@@ -0,0 +1,21 @@
+#pragma once
+
+#include <gtkmm/widget.h>
+#include <gtkmm/box.h>
+#include <json/json.h>
+#include "AModule.hpp"
+#include "bar.hpp"
+#include "factory.hpp"
+
+namespace waybar {
+
+class Group : public AModule {
+ public:
+  Group(const std::string&, const Bar&, const Json::Value&);
+  ~Group() = default;
+  auto update() -> void;
+  operator Gtk::Widget &();
+  Gtk::Box box;
+};
+
+}  // namespace waybar