create helper file for controls reducer (#615)

* initial dataframe commit

* initial dataframe port of core app

* rename variables for clarity

* remove unused import

* comment out unused code

* fix array handling bug in crossfilter dimension creation

* allow creation of empty dataframes

* handle non-existent columns

* handle non-existent columns

* revise tests for new dataframe

* comments for clarity

* comments for clarity

* generate bulk add placeholder with real gene names

* fix bug in gene name adding

* more dataframe unit tests

* fix bug - subset from current world, not universe

* put cut and pasted code into a single function

* improve caching of crossfilter

* remove cascading update bug from graph

* more performance work

* improve state handling for scatterplot

* performance optimization of critical path

* add column summarization

* dataframe utils

* add callOnceLazy

* fix tests

* minor updates found during review

* fix misspelling

* remove RESTv02 from function names

* comment cleanup

* cut/icut col parameter defaults to null

* break up large test

* improve tests and comments on dataframe at/has functions

* add Dataframe withCol/dropCol

* expression varData now stored in a dataframe

* dead code cleanup

* use dataframe.summarize()

* test cases for Dataframe.col.summarize

* update test cases for new dataframe summarize

* improve naming

* use new hasCol API

* add comments

* add more Dataframe.withCol tests

* add ability to specify row index in cut operation

* retire subsetVarData function

* correctly handle expression subsetting

* lint and improve comments

* rename cut to subset

* create helper file for controls reducer

client/src/util/stateManager/world.js

@@ -3,7 +3,6 @@
 import _ from "lodash";
 import { layoutDimensionName, obsAnnoDimensionName } from "../nameCreators";
 import Crossfilter from "../typedCrossfilter";
-import { sliceByIndex } from "../typedCrossfilter/util";
 import * as Dataframe from "../dataframe";
 
 /*