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
Queue messages and handle them sequentially, each time waiting for promises to
resolve before handling the next message.
Updates #1899, which likely happens because an error message is received
before messages have been fetched.
in which you can set user affiliations and roles.
Also, let getAffiliationList return an Error instead of `null` if you're
not allowed to fetch a particular affiliation list.
