Admin can create Agency Admins & Agency Admins can edit details of their own agency

This will allow the super admin user to create users that act as admins for a specific agency.
The agency admins can then edit and review their agency's details. 
i think i need to have the agency_id in strong params somehow, so that the agency_id can be assigned to the user. i did it slightly different in the most recent iteration though (using a .merge)