Horizontal chat (like a news ticker)

[IS2511]

URL query param &horizontal=true. The CSS is currently unfinished so the slide in animation is broken, and message scroll is broken too iirc.

In general I'm not sure how to better animate this. Probably instant when "animate" disabled and quick slide in when "animate" enabled... Can't wait to debug CSS again.

And I also maybe want a "news ticker" animation mode where all messages just scroll past on the bottom (once), and either speed up with more messages or maybe speed is constant and only some messages are picked to keep up (showing recent messages is more important than showing all messages).