Add info commands

[dawnofmidnight]

(part of the Carl ⇒ Ferris migration)

Implement ?server and ?user [id] commands which provide preliminary public information on the server or a user. For the server, this might include creation date; boost count; member status (i.e. number of total and online members); number of text/voice channels and categories; and number of mods/bots. For users, this might include creation/join dates and roles.

Open questions:

• Should we limit ?user [id] to oneself for non-mods?

[troiganto]

The important bits for user info would be: user ID number, user handle, user display name, roles, creation date, join date.

We get most of these info over the moderation view these days, but the info post still serves as a useful log for when we want to look back at an incident and what things looked like in that moment in time.

EDIT: Restricting the user info to moderators doesn't really seem necessary, since all of that info is in the user profile as well.