Revert "Revert plugin to working state from invenio 12"

This reverts commit 9c2ff236a7.

invenio/plugin/custom_invenio_plugin/__init__.py

@@ -1,14 +1,24 @@
 from flask import redirect
-from flask_menu import register_menu
+from flask_menu import current_menu
 
 
 def init_app(app):
     """Initialize application."""
 
     @app.route("/amdmodel")
-    @register_menu(app, ".main.amdmodel", "About AM-D-Model")
     def redirect_to_amdmodel():
         """Redirect to the AM-D-Model website."""
         return redirect("https://am-d-model.eu")
 
+    def register_menu_items():
+        with app.app_context():
+            menu_item = current_menu.submenu(".main.amdmodel")
+            menu_item.register(
+                endpoint='redirect_to_amdmodel',
+                text='About AM-D-Model'
+            )
+
+    with app.app_context():
+        register_menu_items()
+
     return app