It's better to parse an incoming message stanza early, than to have
all kinds of methods throughout the codebase that does querySelector
etc.
Firstly, it allows us to catch and report errors and malicious stanzas early on.
It also simplifies programming because you don't need to try and
remember how to properly parse a stanza, all the work is done upfront
for you.
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.
- Add support for switching ephemerality after message creation
- Move more methods from ChatBox and ChatRoom to utils/stanza.js
- Rename 'ephemeral' to 'is_ephemeral' since it's a boolean
