Resolve additional properties

See #224 and #236.

Deployed to staging, sample requests:

http://staging.api.lobid.org/resource/BT000076559/about?format=full
(#236, here: `TerritorialCorporateBodyOrAdministrativeUnit`)

http://staging.api.lobid.org/resource/HT014976136/about?format=full
(#224, `contributor` details, e.g. `preferredNameForThePerson`)