This also removes an ugly hack, that was needed before.

This also makes long messages unreadable, because we don't shorten long
usernames anymore. We may eventually want to do that again, but it is
hard with translations and we probably want to shorten the displayname
more, as before this change the message was only ever as long as the
timestamp, which is usually just 5 characters...

Update to mtxclient 0.3.0

When user is mentioned (via matrix 'highlight_count'), inactive
rooms will use a different color for the notification circle than
when only general unread messages exist.

Update dark and system themes to provide
colors for the hover states for title, subtitle, and timestamp.

Add room list hover title/subtitle color change support.

fixes #313

fixes #330

fixes #248

fixes #252