Do very simple polling interval grouping

[Poincare]

I have a hunch (developed from looking at the Galaxy UI code) that for lots of applications, most polling queries that we have any hope of batching together will run on the same polling interval. This means that if we just fired the queries with the same polling intervals on the same timer, we'd be able to reap the benefits of batching.

Most of the logic for this has been implemented within src/scheduler.ts already, we just have to fire multiple polling queries in one timer.

[Poincare]

This will have to wait until #385 is merged and I update QueryManager so that it calls an instance of QueryScheduler which will be able to do this sort of grouping very easily.

[Poincare]

This is done with #403.