Add semantic annotations

[thoka]

I would like to be able to add semantic annotations to a document. In its simplest form this would be adding two fields to each annotation: predicate and object, which both could be values or urls into some semantic space (wikidata for instance).

A more advanced form could suggest values from wikidata, depending on user language settings.

[almereyda]

This relates to

• https://github.com/scienceai/web-verse
• https://github.com/edgeryders/openethnographer
• http://indiewebcamp.com/fragmention

and the way how annotator finds anchors.