Fix users list logic editing permissions

[phloreenm]

• [ ] 'admin' should be able to:
  • CRUD other admins and managers
  • I/edit himself
  • 'sysadmin' super-user can't be deleted of edited by any other user
• [ ] 'manager' should be able to:
  • CRUD managers and employees at the same company
  • U/edit himself
  • there should always be at least a manager in the database
• [ ] 'employee' should be able to:
  • R/view other employees at his company only
  • U/edit himself