Multiquery optimization

[cbizon]

Right now, multiquery uses a shared cache, but that's not clearly a win because the cache is at the request/response level. That might work ok for the first hop, but rarely beyond that.

Another point worth considering:
Sometimes we will have a rule like (Pinned)-[related to]-(?)-[p1]-(?). and a different rule like (Pinned)-[associated with]-(?)-[p2]-(?). In this case, associated with is a subclass of related to, so running the associated with query in principle adds no new information and can be dispensed with.