Implement sort of series in row col Chart

[Brian Lewis]

The exam dashboards (and later the school accreditation dashboards) require series to be displayed in a hardcoded order.

Support this through the columnSortBy and columnSortDescending bindings

Refactor exam results by benchmark to use this, rather than resort the series in the onChartRender handler.

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[Brian Lewis]

feat(charts): row col chart supports sorting of series

Resolves #833

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