* immutable crossfilter
* first cut at reducer refactor with cascade model
* add initial redo/undo implementation
* small optimization
* integrate expression with history
* add tests for new reducers and fix a couple of small initialization bugs
* treat tiny lasso selections as a clear
* better function name for clarity
* fix undo for differential expression
* remove logging
* fix regression due to bad merge
* cleanup and comments for clarity
* improve undoable configuration for flexibility
* fix stale comments
* remove debugging code from production build
* rename categoricalSelectionState
* rename file
* improve comments
