Reuse filters

[domoritz]

Many of the charts use the same filters. Every chart is filtered by brushes in any other chart. If there is only one brush, we only have two filterings. This means we could reuse the filtered datasets instead of filtering again for every column.

In https://github.com/uwdata/falcon/blob/b3a4a6d6f5edd2063c08e8e9c15227dfecc8e11d/src/db/arrow.ts