[A11Y] Discussion reply count (mark as read) is button with no accessible information

[davwheat]

While having these as buttons make sense to visual users, using ChromeVox allows us to hear what a screenreader user will hear:

test general flarumite replied 8 days ago

1 button

Preferably this should be "1 reply". Multiple replies should be "3 replies". The unread version should be "1 new reply. Mark as read.".