Add `location` parameter and polygon support for queries and facets

See https://github.com/hbz/lobid/issues/88

Pass space delimited `lat,lon` points describing the polygon.

Samples:

`/resource?author=136378153&location=52,6.5+52,7+51,6.5+51,7`
`/resource/facets?field=@graph.@type&location=52,6+52,7+51,6+51,7`
Merge pull request #89 from hbz/location

Add `location` parameter and polygon support for queries and facets