add role Challenge-admin

[kikmann]

not overall admin but challenge admin

[kikmann]

• [x] where to store role ? challenge-X-user
• [x] how to set roles ? setup->users - challenge-admins can set admins

[kikmann]

~- [ ] set role on creation to user~ not required

[kikmann]

use role for actions - potentially for all under the Setup Menu:

• [x] general setup
• [x] users
• [x] trainings
• [x] specials
• [x] teams