- Modernize the `RegisterPanel` component and turn it into a Lit element.
- Improve CSS and move into plugin.
- Fix button click handler not being registered.
- Fix switching between login/register form after logging out (Fixes#1556)
Importing a plugin's `index.js` file from other plugins means that it's no
longer possible to remove that plugin by removing it from `src/converse.js`.
Instead, all plugins need to be imported in proper order from
`src/headless/headless.js` and `src/converse.js`.
Updates #3026