Implement access control

[uniqueg]

FOCA now adds support for Casbin-based access control on the development branch. Configure access control for the ELIXIR Cloud Registry in the following way:

• Anyone has read permissions (i.e., they can access all GET endpoints)
• Any authenticated user can create (POST) resources (i.e., add services); they may be able to use PUT as well, as long as a resource with that ID does not yet exist
• After creating a resource, a user becomes a resource Owner
• Resource Owners can edit (PUT) and delete (DELETE) existing resources
• Resource Owners can change the permissions of other others: in particular, they can make other users Owners or Maintainers
• Resource Maintainers can edit (PUT) but not delete (DELETE) existing resources