DE release documentation

[mmontesanonyc]

On feature-chart-printer we have a series of Data Explorer enhancements, covering:

• x-axis labelling - using a temporal data field for the x-axis, and a nominal data field for the labels, and removing duplication from the x-axis.
• Revising colors, using viridis for maps and magma-derived colors for trend and scatterplots. (This obviates a need for rankReverse in map colors.)
• improve trend chart - using a spec that has hover labelling, single point tooltips, and removes interaction from the x-axis. This also includes a special test for AQ Action Days which use a nonstandard grammar around measurementType, so improve labelling for those indicators. This spec also removes the legend, which raises the issue of screenshotting/printing, so...
• chart printer - create a 'save chart' option that generates a print-ready/save-ready version. This does things like adding the legend to the trend and links charts, adding the year to the map, and adding all the notes and source to the image. This also improves the footer with the new options, including de-duping Source printing for all views.
• revise bars to dots for means as an add-on.

[mmontesanonyc]

PR opened, planning to deploy shortly, closing issue.

[mmontesanonyc]

With #1146, also re-adding "No Compare" functionality. Bit of a layering issue here, which I couldn't sort out, but I re-styled the line so it looks ok.