Add 'show more replies' + counter to "sub" comments.

I have been noticing that the sub comments sometimes get so large and with so many, it's cluttering the whole topic.

Some 'load more comments' for the sub comments would be nice. As well showing how many sub comments there are.

Also like the way NodeBB for example "groups" the sub comments together but also shows them on the main thread. It is much easier to read through.