Streamline using and creating themes

[YakovL]

This is a complex issue to elaborate. Let's take this post as an inception.

Goals:

• Currently, switching themes is not a clear process; ultimately, it should be as simple as using a select control that lists all the available themes (see also SwitchThemePlugin);
  • This also requires a convention (should a theme have a systemTheme tag to be recognized? otherwise, how to recognize them?)
• Exploring existing themes is not straight-forward, although there's TiddlyThemes. There should be no UX gaps – the index should be easily explorable from TW's UI (or docs, but that's less desirable, or at least should complement UI);
  • Also, many old themes should be repacked as actual themes;
  • Themes should probably be packed into a collection, too, for smoother UX, but that's more optional;
• The docs regarding themes are incomplete to say the very least; instead, it should be clear how to create a new one.

Challenges:

• A custom StyleSheet can be included into a theme (to keep user adjustments), but refreshing is not invoked after StyleSheet is edited (one have to edit the theme/reload);
• ColorPalette is not a part of a theme, right? How to pack them together? Should we include it into themes and should we allow to set a theme but then change CP separately (like for dark mode)?