Align message container to the bottom

[xPaw]

Fixes message jumping when all the messages are visible without a scrollbar and new messages load in (if there are 90 condensed messages, there are only a couple of lines visible). Also makes it much nicer with lazy-init when there's only 1 message visible.

This pretty much matches behaviour of other chat apps where they begin stacking from the bottom.

[astorije]

Trying it locally, it feels super weird to me lol, but it's probably > 80% because I'm used to the current way.
Objectively speaking, the advantages sound reasonable and I don't see any red flags UX-wise.
Let's give it a chance and see how it's received :)