Move facets route to Lobid API

See https://github.com/hbz/nwbib/issues/33 and https://github.com/hbz/nwbib/issues/20

Deployed to staging.

Simple sample:
http://test.lobid.org/resource/facets?field=@graph.@type

Filter by subject and name, specify size:
http://test.lobid.org/resource/facets?field=@graph.@type&subject=http://purl.org/lobid/nwbib-spatial%23n99&name=Wittgenstein&size=5

Used by NWBib on staging for faceted search: http://test.lobid.org/nwbib