Explore making chunkers more responsive.

[tshead2]

It takes a surprisingly long time to retrieve chunker metadata from the CCA page, despite the fact that we only load data on-demand. See what's taking so long, and whether there are opportunities for improvement.

[tshead2]

We're now at a point where metadata requests always return quickly, because they can be handled before the rest of the data is loaded by a chunker. Also, all of our chunkers operate by loading individual columns/attributes on-demand, so data that isn't requested won't be loaded.