Task/395 pagination queries

### Description
Pagination implemented and with rudimentary unit tests.
URI params 'offset' and 'limit' used.
A third URI param 'details' steers whether 'mongo db count' command is issued on no hits.

I think this comment is obsolete... After our last converstation, we conclude that `details=on` always returns the count in the StatusCode response, no matter if sucess or fail.