This will make it easier to add config-based functionality, such as
allowing/showing the `/topic` slash command only to those users who are
allowed to set the subject.
- Use flexbox where possible
- Simplify header by using `justify-content` instead of setting column widths
- Show description below the row containing the title and buttons
- Add config variable `muc_show_logs_before_join`
- Restore nickname form for the original use-case (when not showing MAM logs before joining).
- Render nickname form in the `.muc-bottom-panel` when showing MAM logs (instead of in a modal)
- Show a message when there aren't any archived messages to show
- Fix converse-mam so that chat logs are properly fetched before entering a MUC
closes#1266
- 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
