Only allow super-admins to add/change/remove site logos
Only allow super-admins to add/change/remove site logos

Resolves: https://dxw.zendesk.com/agent/tickets/10487
Resolves: https://trello.com/c/8AOwXyCE

dxw/govuk-blogs,dxw/govuk-blogs,dxw/govuk-blogs