add nominatim wrapper

[WolfgangFahl]

Is your feature request related to a problem? Please describe.
Geograpy allone can often not find places. Comparing with other services such as nominatim is useful in such cases.

Describe the solution you'd like
Allow nominatim queries and "voting" as an option

Describe alternatives you've considered
Other services might also be used but nominatim is preferred since it provides wikidata id of locations on request.

Additional context
In the ConferenceCorpus / ConfIDent project this feature has already been tested