Action description: return concrete links to resources only for objects, not for lists
Action#resourcify: translate value_id and value_label to db_name

This ensures that parameter names used for API I/O have
different names in database (compatibility reasons).

When referencing a resource, it must have implemented action show,
as its output param list is used for the translation.
Authentication providers

Define an interface for creating authentication providers, that are
self-described. Client can choose what method it understands
and/or wants to use.

HTTP basic and token auth are built-in. They need to be subclassed
and the developer must implement methods to find user, tokens, etc.