- Fix choosing of a categoy
- Make the highlight color darker (more visible)

Also, listen to the `focusin` and `focusout` events, since they bubble,
allowing us to listen on the chatbox itself.

- Use async/await
- Wait for devices to be created before continuing

to rely on the parsed stanza attributes

This was to fix a bug whereby a full stanza was used to query for 1:1
messages with a full JID when the bare JID is stored.

We now are sure that the attributes we're using to query for duplicates
are the same attributes that get saved for a messages.

* Use lit-html
* Let it look and behave similarly to other list views in the controlbox

* Remove backbone as NPM deps and from docs
* Remove backbone stuff from webpack

and replace with button to open invite modal

* declare picker events in lit-html
* init intersection observer only once
* don't set value manually
* don't manually add classes
* avoid x-scrollbar and 'undefined' in search input

before creating any new ones