Who are the users who have this ability?

[cellio]

Users can earn abilities (or have them granted by moderators), but this information is not visible in the aggregate:

• As a user, I sometimes want to know who/how many can close questions or edit or create tags. Short of guessing my way through individual profiles, I can't find that out.
• As a moderator, I want to be able to evaluate the thresholds for earning abilities -- how are we doing with natural grants, and should I ask the admins to lower the thresholds? Again, I can't tell.
• As an admin, I want to be able to answer the same questions as moderators but across the whole network.

I'd like us to have a place in the UI where you can, for each ability, see all the users who have it. I'd also like to be able to highlight recent awards somehow -- a "new" badge next to the user or listing them by date earned or something. Higher abilities, in particular, are rare and it would be nice if we could announce them somehow. Think of it as a small bit of public thanks and acknowledgement for users who've contributed a lot.

This is a broad request that needs to have a lot of design details worked out.

[cellio]

I propose to add a "users with this ability" section to the pages describing individual abilities. (Entry point is app/views/abilities/show.html.erb.) This would involve a controller change that I think would be similar to the one done for #1409, where we start from a user and get the list of all community profiles for that user. Here, we start from an ability and query users looking for that ability. (Unless someone knows a better way to do it?)

Because that query could get expensive at scale, we should wait for #1411 and then do something similar to cache users on abilities.

This doesn't address identifying and somehow highlighting new abilities.