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.

So style guide only allows two possibilies:

* `T* t`, if the argument is used to return someting
* `const T& t`, if the argument is only to be read inside the function:

Corolary: `T& t` is always forbidden.

Is that correct? (I'd like to know, for using the same criteria)