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.

Good! connection->count() and connection->query() are done within the same "block" of mongo driver semaphore take/give. That way, we minimize the posibility of some other Orion client alter the count before query is resolved (we elimininate that possibility completely in the case of mono-Orion deployment, but in horizontal scaling scenarios, with several instances of Orion running in paralel the posibility exist... no worries by the moment, anyway).

NTC