DataTask Scheduling Dispatch

[Keith-Bateman]

Is your feature request related to a problem? Please describe.
Somewhat related to the aggregation in #21 , we need a policy to make decisions about when to send DataTasks to the scheduler from the client (as they can be cached for purposes such as aggregation).

Describe the solution you'd like
Some sort of aggregation-by-need policy would be interesting to explore here. I/O can conceivably be delayed until it's requested by a read. It'll have to be compared to non-aggregation and aggregation-by-size.