Migrate dc Charts and dependent dashboards to echarts

[Brian Lewis]

dcjs provides close charting integration with Crossfilter.

However, to standardise on a single charting platform, it makes sense to remove dc and use echarts in its stead.

By recreating the connectivity between crossfilter and charts built from echarts, we get:

• a single chart platform
• the greater flexibility of echarts over dcjs
• ease of use
• remove dependency on d3

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[Brian Lewis]

feat(charts): migrate school and teacher dashboards to echarts, refactoring

Resolves #838

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