Flag/highlight new posts in the forum

[stpaultim]

We got this feature request for the forum in Gitter today:

I really need new-message indicators on the forum, and don't know if they don't exist or they're not turned on.

[jenlampton]

I've added the new marker to the taxonomy/term view: https://forum.backdropcms.org/forum/how-and-troubleshooting

I'm going to close this ticket, but please re-open if it turns out we need them anywhere else!