Include object URIs in the Solr index
Searching for URIs in metadata is currently not possible.
It would be nice to have a field called 'objectURIs' that contains all URIs that appear in object position. For completeness it would also be nice to have 'predicateURIs' and 'subjectURIs' although it is harder to find situations where these two fields would be needed.
Note that the containing entrys resourceURI should not be included in the 'subjectURIs' as it is already contained in the 'resource' field.