feat(neon_talk): Add room list

[provokateurin]

Extracted/rewritten from #366
Towards #356

[Leptopoda]

Mostly UI stuff and some minor code style.
I know that you are trying to get things done one step at a time but let's try to also do the UI right from the beginning.

[provokateurin]

I implemented the unread indicator a bit different than you suggested, but I think it works pretty well this way.
Please note that the actual rendering of the message is not implemented yet (e.g. mentions or files won't work). That will be done in a different PR when the actual chat layout will be implemented.

[provokateurin]

Hm should the indirect mention also show the @? I'm not sure how this is best handled, as @room can sometimes be very important and sometimes be used for no good reason. Maybe this should be implemented as an option to be let the user chose what they prefer.

[Leptopoda]

You forgot to assign the subscription.
Other than that let's get it done.