Get images from Wikidata/Wikipedia

[fsteeg]

Suggested by @jschnasse, e.g. for http://test.lobid.org/authorities/118540238

[acka47]

There are different options to implement this.

1. The easiest one is to query the MediaWiki API like described in https://stackoverflow.com/questions/37181391/how-to-get-the-default-image-of-wikipedia-article
2. Another option is to add wikidata links to the GND data. This has the advantage that we can also add links to wikidata based on wikidata itself. (Wikidata has >500k items with GND ID while GND has only 425k links to Wikipedia.)

BTW, of the 500k items in wikidata with a GND ID, currently ~190k have an image, see http://tinyurl.com/yazatkdb.

[acka47]

We can get the links directly from entityfacts (on-the-fly for the beginning), see #44.

[fsteeg]

This is part of #44, closing.