Simplifying themes

[tonyaellie]

We currently have a lot of themes. That diversity is nice, but it has two problems: - Maintainers and contributors can’t keep all themes well-tested, so contrast/accessibility issues slip through. - Visual regressions become harder to spot and fix across themes.

My proposal:

1. Shrink the default theme set to 3-6 curated themes.
2. Provide an in-app/custom theme editor so users can create/save themes that sync between devices.
3. Move the existing themes into a 'Legacy themes' section (with a warning that they might not meet current accessibility standards and have other issues).

Would love to hear people's thoughts on this and what themes they use.