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.

Well, it is only a part of the whole story.
In case nothing is found, because of URI parameter "offset" AND 'details' is set to 'on', the details of the errorCode will contain a text explaining the count vs offset.

If something is found AND details='on', then the count will be added as the 'details' part of the errorCode of the '200 OK' response.

What is missing is perhaps a comment about the '200 OK' + details='on', later in the code ...