[JSONMenu] Provide a Spoon to render menus based on JSON files

As an user I want to have a Spoon that renders menus based on JSON files so that I can add new custom user-menus without programming effort.

Acceptance Criteria:

- The menu is able to render the main menu level
- The menu is able to render an optional sub-menu level
- The menu uses URLDispatcher as dispatcher
- The menu provides a refresh mechanism to avoid get eaten by the garbage collector