* Add x and y column picker to line graph
* Use column selector in heatmap options
* Add column selector to histogram
* Add column selector to scatter plot
* Fix tests
* Add xColumn and yColumn to data structure in line graph tests
* Move scatter container defaults to visSwitcher
* Add fillcolumn validity checking to histogram
* regularize XYcontainer and render it and lineplussingle stat in visSwitcher
* Initialize all views with null columns
* Place Line and Scatter Options x-y column selector behind cloud feature flag
* Rename getGroupableColumnSelection
* Add defaults to x/y column selections in line graphs
* Add defaults to x/y column selections in scatter
Christopher Henn
Deniz Kusefoglu
Jade McGough
zhulongcheng