Only indent replies if neccesary.

Right now each reply is indented a bit, which can be good for readability with long threads and branching conversations, but for simple conversations it might be better to just put one reply below the other. Otherwise a long chat might get indented a lot, wasting space unnecessarily.

The solution would be to only indent replies if there are multiple replies to the same post, basically like the client already does with threads.

Here an example of a longish, single-threaded conversation. Each post gets more and more indented