Feature/#96 arbitrary polygon support

Created by: hixi

This adds countries back to the frontend. You cannot cut out countries in the current state this is in, because it is still missing the multipolygon-json-backend-client that is needed to receive such a request.

Review is possibly easier from #751db86 and #4a5a0c5

Reviewed by:

• @das-g

Created by: das-g

Should we also place a license file for the production *.poly files? (Did we have one in osmaxx-conversion-service? Under what terms did we obtain the boundary data?)

Created by: hixi

License file(s) would be a good idea, but AFAIK we had none so far, so we should probably track, where they came from in the first place (I think they were from Wambacher, but we definitively should check that).

Created by: hixi

closing, already included in #475