Create a stacked RowChart object in dcCharts to handle gendered display [2020:O]

[Brian Lewis]

Currently our dc row and bar charts support single value display - stacked charts require additional accessor functions to be passed in.

Create a stacked bar in order to split gender in the chart display.

Note 'minor' but marking as lower priority for now.

[Brian Lewis]

@ghachey fyi

[Brian Lewis]

Implemented for bar charts in Issue #509 29 September commit 88e1e36

[Ghislain Hachey]

@Brian Lewis this was implemented for bar charts as stated here. But the school dashboard still does not handle gendered display with legend and 2 colors as discussed in #563