Collection list endpoint

[jgonggrijp]

This is an RDF endpoint (#157) where clients should be able to

• Send a GET request to get a list of the collections that exist (sourced from the edpop:collections graph, see Graph and namespace organization #156).
• Send a POST request to create a new collection.
  • The creator determines the IRI of the collection, which ends in a short name. For example edpop:collection/almanacs. This IRI is already used in the request payload, so there is no need to work with blank nodes.
  • The request fails if a collection with that IRI already exists.
  • Creating a new collection should specify to which usergroup the collection belongs. The user must already be a member of that research group.
  • Possible alternative: create a collection that does not belong to a research group but which is private to the user (though maybe still visible for other users).