Added way to get sub user totals

[Carter4242]

I closed the last pull request and made a new one that's probably not the way to do things though...

I think it's important for this to get added to show the sheer scale of what is happening here. I don't write websites or js code, but this was super simple. Could someone please review this test it and add it to the front end?

The way this works is it uses the category of the sub from ModCoord, and then from there, you can have a low estimate of the total number of users affected by the priviating of subs, which can be updated in real-time without requests to the Reddit servers. If you wanted to you could also add every sub up to get the total users affected if all subs were closed.

Thank you so much!