Improve accessibility, specifically for color-blind folks

[jeroenheijmans]

There are accessible descriptions of all visuals. But there's also a bunch of people who can't distinguish colors well enough, while still seeing the graphs. We can easily improve things for them:

• Consider using pointStyle for line graphs (and their legends)
• Consider using fill patterns for bar charts (and their legends)
• Consider making one of both of those optional as they might hurt accessibility for other folks because of the clutter it adds?

[jeroenheijmans]

Point style for line graphs was added in 2022. The fill patterns will have to come later (it also has to be pretty of course!), if someone wants to propose a PR I'm open to that.

[jeroenheijmans]

This library could be included to fix this!

<script
  src="https://cdnjs.cloudflare.com/ajax/libs/patternomaly/1.3.2/patternomaly.min.js"
  integrity="sha512-Zjnjh2DCl/MrwdZ8FNp25vSbXac3yWUWoMn0CL8qQ/K11HGv7cJ9RGNUiojnSfqVtwbGf+eyqEEjiw2hlHd6iQ=="
  crossorigin="anonymous"
  referrerpolicy="no-referrer"
></script>

It allows for using pattern.draw('square', rgbaColorHere); as backgroundColor values.