Discussion fixes

- partial fix for reply button causing the screen to jump randomly
- fix for reply box meta
- min height for empty discussions
- removing reply-to author for top level comments in threaded view
I'm confused why `responseTo` is incorrect for unthreaded. Are we sure that the API is returning responses differently for unthreaded? If possible, all these discussion sub fragments should not care whether the discussion is threaded or not. That's just a styling/ordering thing.