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
Had to make various other changes due to incompatibilities.
- Use the new `lit` package instead of `lit-html` or `lit-element`
- Drop `haunted` since it breaks the rules by specifying `type: module`
but then doesn't import with file extensions
- Use Sass Dart instead of node-sass (fixes#2445)
- Upgrade Karma
- Move top-level functinos to utils files
- Get rid of unused/obsolete overrides
- Only import components there where they're used
- Bump version in package.json
The eventual goal is to avoid UI-related stanza processing if the relevant chats
aren't in the DOM.
With the current architecture, chatboxes are created (and the stanzas
related to them processed) even if `#conversejs` isn't in the DOM.
* Initial work on making controlbox an element
* Create a shared base class
* Ceate ChatBoxViews proxy
* Update sass now that certain classes are moved to converse-chats element
