Create stubs for the music picking menu (SuperTux#2617)

src/gui/item_music.cpp

@@ -0,0 +1,19 @@
+#include "gui/item_music.hpp"
+
+#include "gui/menu_manager.hpp"
+#include "gui/menu_music.hpp"
+
+ItemMusic::ItemMusic(const std::string& text, int id) :
+    MenuItem(text, id)
+{
+}
+
+void
+ItemMusic::process_action(const MenuAction& action)
+{
+    if (action == MenuAction::HIT) {
+        MenuManager::instance().push_menu(std::make_unique<MusicMenu>());
+    }
+}
+
+/* EOF */

src/gui/item_music.hpp

@@ -0,0 +1,18 @@
+#ifndef HEADER_SUPERTUX_GUI_ITEM_MUSIC_HPP
+#define HEADER_SUPERTUX_GUI_ITEM_MUSIC_HPP
+
+#include "gui/menu_item.hpp"
+
+class ItemMusic : public MenuItem
+{
+public:
+    ItemMusic(const std::string& text, int id = -1);
+
+    /** Processes the menu action. */
+    virtual void process_action(const MenuAction& action) override;
+
+};
+
+#endif
+
+/* EOF */

src/gui/menu_music.hpp

@@ -0,0 +1,13 @@
+#ifndef HEADER_SUPERTUX_GUI_MENU_MUSIC_HPP
+#define HEADER_SUPERTUX_GUI_MENU_MUSIC_HPP
+
+#include "gui/menu.hpp"
+
+class MusicMenu : public Menu {
+public:
+    MusicMenu();
+};
+
+#endif
+
+/* EOF */