Access control: Create editor and member coach role

[ManuelMoeri]

After CanCanCan has been setup (#946) the new roles can now be created. These two roles are the 'editor' role and the 'member-coach' role. Feel free to change the names of them if you think it's not fitting enough.

Editor The editor can edit every profile in the application.

Member-coach The member-coach can edit profiles of people that are in the department he is member-coach off.

TODO

• [ ] Create roles as defined above
• [ ] Tests