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 you mean that

```
connection->count(getEntitiesCollectionName(tenant).c_str(), bquery);
```

"destroys" the first argument?

It's weird, as I use the pattern `connection->funct(getXCollectionName(tenant).c_str(), ...)` all the time in mongoBackend...