Refactor: Setup admin data via events

- Move admin menu setup to a new event `Croogo.setupAdminData`
- Update existing usage of CroogoNav::add() to ass the menu name implicitly

Closes #364
Use CroogoHelper to display top admin menus

- Configure top admin menu in CroogoComponent (we can't use events in
  Croogo plugin)
CroogoHelper to accept divider, icon => false, before and after
BCBREAK: Remove old superfish initialization code