"- Properly handle message correction being received before the corrected message"
was there twice

- Fixes #1575. Height not properly set on MUC invitation list
- Add new configuration setting: `muc_mention_autocomplete_min_chars`
- Bugfix. `min_chars` setting for MUC mentions wasn't having an effect

Unfortunately this doesn't work on Firefox and there's no proper
workaround. https://github.com/philipwalton/flexbugs/issues/108

Reverts:

Revert "Bugfix. Properly insert error messages and spinner"
This reverts commit 6a419cc1.

Revert "Use flexbox to keep the chat scrolled down"
This reverts commit dd91d3cc.

when the textarea contains an unsent message

now that messages appear in reverse order due to flexbox

By using `display: flex` and `flex-direction: column-reverse`, the chat
now automatically scrolls down when loaded, without requiring any
extra JavaScript.

We still need to scroll down with JavaScript when sending a message.

By using `column-reverse`, the messages container now works in reverse.
So the newest message is the first element in the container and the
oldest message is the last. This is the reverse of before.

Due to this, this change will likely break some plugins.

It gets populated again upon MUC reflection or chat marker

Up and down arrows only serve as message correction shortcuts if the
textarea is empty.

This means that:

- Up arrow doesn't start correction of previous message if we're currently writing a message
- Down arrow doesn't erase currently written message

This is based on user-feedback and is also how Slack handles these
shortcuts.

for limiting messages to a certain number of characters.

For some reason the latter causes extreme lag when switching rooms

Removed one occurrence

When reconnecting with a new transport, we call setUserJID
so that a new resource is generated, to avoid multiple
server-side sessions with the same resource.

We also call `_proto._doDisconnect` so that connection event handlers
for the old transport are removed.

- Don't ever resume SMACKS stream when using BOSH
- Clear SMACKS session data when using BOSH

https://xmpp.org/extensions/xep-0198.html#resumption

The <resume/> element MUST include a 'previd' attribute whose value
is the SM-ID of the former stream and MUST include an 'h' attribute
that identifies the sequence number of the last handled stanza sent
over the former stream from the server to the client.

- Set roster_fetched flag when we get an empty IQ[type="result"] stanza
- Set `restored` flag when resuming in converse-smacks
- Don't trigger change event when fetching xmppstatus values
- Removed two events, since we can just listen to `change` on `_converse.xmppstatus`.

- Test for info message indicating a configuration change
- Test that the MUC reconnects when a `not-acceptable` error is returned