Undo/redo (#659)

* 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

client/src/components/continuous/continuous.js

@@ -9,10 +9,10 @@ import * as globals from "../../globals";
 import HistogramBrush from "../brushableHistogram";
 
 @connect(state => ({
-  obsAnnotations: _.get(state.controls.world, "obsAnnotations", null),
-  colorAccessor: state.controls.colorAccessor,
-  colorScale: state.controls.colorScale,
-  schema: _.get(state.controls.world, "schema", null)
+  obsAnnotations: _.get(state.world, "obsAnnotations", null),
+  colorAccessor: state.colors.colorAccessor,
+  colorScale: state.colors.scale,
+  schema: _.get(state.world, "schema", null)
 }))
 class Continuous extends React.Component {
   constructor(props) {