R1:f190c42bcd2e

Store charts earlier and build them out a little later

Summary:
Ref T13279. Currently, we store a fairly low-level description of functions and datasets in a chart. This will create problems with (for example) translating function labels.

If you view a chart someone links you, it should say "El Charto" if you speak Spanish, not "The Chart" if the original viewer speaks English.

To support this, store a slightly higher level version of the chart: the chart engine key, plus configuration parameters. This…