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
- Update to the latest @converse/skeletor (which uses mergebounce to batch writes)
- Flush storage before logging out
- Flush when reloading the tab
- Create initStorage method
Update storing of app settings. Store settings in a closured
`app_settings` object inside `@converse/headless/shared/settings`
Remove the `_converse.settings` object.
