[GSoC] Improving the theme editor experience

[pigeonflight (David Bain (Will Theme Plone Sites))]

I'd want to add this to a UX category but User Interface will work.

I just put this together based on recent experiences using the theme editor:

Issue: Improving the theme editor experience

[pigeonflight (David Bain (Will Theme Plone Sites))]

In terms of experience, this is what we're competing with --> https://codepen.io/project/editor