Add a "show all" button to nested comment section

[lsabor]

Add a "show all" button to nested comment section.

User exmateriae suggests:

I had to click 9 times to see the comment was "Thank you" lol, it would be nice that after 3/4 levels, a "open all" button appears.

The particular comment is here: https://www.metaculus.com/notebooks/40220/the-rand-x-metaculus-policy-challenge-live-event/#comment-516455

If you navigate to the page without the #comment-516455 suffix, then you'll have to hit the "show X replies" over and over. https://www.metaculus.com/notebooks/40220/the-rand-x-metaculus-policy-challenge-live-event/

Possible solutions (assigning to @SylvainChevalier to pick which one, reassign, or reject the ticket):

1. add a "show all replies" button if the hidden replies are more than 1 level deep
2. keep "show X replies" but just have it completely unfurl the conversation
3. somewhere in the middle like "show X replies" unfurls 2 levels deep or the 3-5 most recent replies (inspired by the reddit system)

[SylvainChevalier]

Let's go with:

2. keep "show X replies" but just have it completely unfurl the conversation

By far simplest. Also more coherent with the literal words: currently "show 3 replies" only shows 1.

[lsabor]

User darkives suggests:

Another way to cut down on clicking might be to have unread nested comments shown by default while read nested comments are hidden by default.

[SylvainChevalier]

have unread nested comments shown by default while read nested comments are hidden by default

Counterpoint from slack:

I don't think this works. Imagine you visit a popular question for the first time and you have to scroll a ton just to get to like the 3rd comment.