Replace OCLC URIs with Wikidata ones

[rybesh]

OCLC no longer published linked data. We can keep the links to Worldcat but should no longer use them as the subjects of triples. Hopefully we can use the OCLC control number property to do the mapping pretty easily.

[rybesh]

OCLC has restored its linked data but we still might want to consider doing this.

[rybesh]

This has now become more urgent, as OCLC now considers linking to their catalog data to be a form of “hacking attack” and is suing individuals who do so. Since PeriodO data currently links to WorldCat catalog data, we must assume that we too are in legal jeopardy and remove all traces of OCLC / Worldcat URIs from our dataset.

Fortunately this will likely result in more robust data, as OCLC catalog data is quite poor quality in comparison to alternatives like Wikidata.