Record serializers need to include a link to the bucket

[lnielsen]

See how to create a record and a file: inveniosoftware/inveniosoftware.org#106

Currently when you create a record the response looks like this:

{
  "created": "2019-08-01T09:21:47.261207+00:00",
  "id": "2",
  "links": {
    "self": "https://127.0.0.1:5000/api/records/2"
  },
  "metadata": {
    "contributors": [
      {
        "name": "Doe, John"
      }
    ],
    "id": "2",
    "title": "Some title"
  },
  "revision": 0,
  "updated": "2019-08-01T09:21:47.261214+00:00"
}

It should look similar to this:

{
  "created": "2019-08-01T09:21:47.261207+00:00",
  "id": "2",
  "links": {
    "self": "https://127.0.0.1:5000/api/records/2",
    "files": "https://127.0.0.1:5000/api/records/2/files/"
  },
  "metadata": {
    "contributors": [
      {
        "name": "Doe, John"
      }
    ],
    "id": "2",
    "title": "Some title"
  },
  "revision": 0,
  "updated": "2019-08-01T09:21:47.261214+00:00"
}

Adding the links.files properties.

[lnielsen]

Needs to work for both the landing page (/api/records/1 and search results /api/records/)