Load new posts above the viewport without user action and change the "New posts" button to scroll to the top

**Problem**
I want to see/read new posts without the scroll/reading position being forced to the newest one, so I can keep reading from the position I was at.

**Suggested solution**
I would prefer the client to load new posts above the view automatically without any click action. The "New posts" button could then change functionality to simply scroll to the top if clicked.

Whether people prefer to read from their existing position, or see the newest posts, the suggested solution supports both preferences in a minimalist way that doesn't add more UI than there currently is. It is also how Twitter and various other clients do it. I'm not one to suggest copying Twitter for the sake of it, but in this case I think they have the most elegant and functional solution.

**Alternatives considered**
I've considered the existing suggestions here:
https://github.com/cheeaun/phanpy/issues/419
However, none of them offer the same functionality and flexibility.