Add an API for CRUD operations on collections

[joachimvh]

My suggestion for a Collection API. The documentation file describes how it works. It works similar to the policy API as in that a GET to the root returns information on all collections you can modify, POST to the root for new collections, etc. PATCH is not supported, only PUT to replace a collection.

You can only create an asset collection over resources you are the owner of.

You can only create a party collection if you put yourself as one of the owners (that can modify this collection).

Automatically generated collections, through relations, can be read but not modified.

Example JSON bodies for the POST request:

{
  "description": "My assets",
  "type": "asset",
  "parts": [ "http://example.com/alice/", "http://example.com/alice/README" ],
}

{
  "description": "My party",
  "type": "party",
  "owners": [ "http://example.com/alice/profile/card#me" ],
  "parts": [ "http://example.com/alice/profile/card#me", "http://example.com/bob/profile/card#me" ],
}

A corresponding response to the GET request would then be something like

@prefix dc: <http://purl.org/dc/terms/>.
@prefix odrl: <http://www.w3.org/ns/odrl/2/>.

<http://example.com/collections/123456> a odrl:AssetCollection ;
  dc:description "My assets" ;
  dc:creator <http://example.com/alice/profile/card#me> .
<http://example.com/alice/> odrl:partOf <http://example.com/collections/123456> .
<http://example.com/alice/README> odrl:partOf <http://example.com/collections/123456> .

<http://example.com/collections/654321> a odrl:PartyCollection ;
  dc:description "My party" ;
  dc:creator <http://example.com/alice/profile/card#me> .
<http://example.com/alice/profile/card#me> odrl:partOf <http://example.com/collections/654321> .
<http://example.com/bob/profile/card#me> odrl:partOf <http://example.com/collections/654321> .