geosketch runs are redundant

[patrickjdanaher]

This costs us a few mins of runtime, and should be fixed when convenient.

Details:

• geoSketch has two parts: it lumps cells into "plaids", and it samples from the plaids.
• The first part only needs to be run once, but we're running it every time we subsample

Solution:

• run geoSketch once, and save the plaids
• then replace all current geoSketch runs with a simple subsampling from the plaids
• (This should be implemented as a function excerpting the subsampling code from geoSketch)

[patrickjdanaher]

done. in ADO.