Fixed by showing the participants sidebar hide button on larger screen
sizes as well.

Users can only be muted in moderated rooms

* Make the emoji a little bit smaller
* Avoid scrollbar appearing for single emoji messages
* Also identify single sent emojis

We need it for mobile where (eventually) we might have the participants
sidebar occupy the whole screen.

Fixes scrollbar appearing next to spinner when logging in.

* Add test and changelog entry
* Also show message subject if available

This now requires `sendMessage` to return a boolean to indicate success.
Disable the textarea while message is being sent.

When OMEMO isn't possible, render it as grey.

This change makes OMEMO for MUCs easier, since there I anticipate that
OMEMO support might change dynamically based on who enters/exits the
room.

updates #1180