Add a GET request for searching local authors

This is intended to be used by remote servers to search our authors.

URL: <ourhost>/api/search?query=<querystring>

Empty or missing query string returns all authors. Authors are returned
as a json list of the following format:

[
 {"url": <author url>,
  "host": <our host>,
  "displayname": <author username>,
  "id": <author GUID>},
  ...
]

API tests have been updated.