(PDB-1071) Add pagination to service query method

In order to support pagination in the service query method, have it
accept a map instead of the raw query structure.  The map should contain
a :query referring to the original query, alongside (optional)
:order-by, :offset, and :limit members.
I'm fine with either, though I implemented the combined option because (assuming I didn't misunderstand) I thought that's what @senior preferred -- perhaps with an eye toward the (eventual) possibility of a more sophisticated query syntax, one that superceded the :limit/:offset/:order-by options?

But I also noticed the mismatch you mention.