This is largely a leftover from the Backbone.View days and makes less
sense now that the UI is componentized.
Ideally we don't want to call commands on the "views themselves, instead
we should be working on the the models and let the "views" update
themselves automatically.
Also, given that the `jid` attribute on the chat views might change,
especially when rendered declaratively in other frameworks like React,
a view might not be available at times where we previously might have
expected it to be (since it's been repurposed for a different JID).
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
