add list of moderators to top of Tavern chat

Add moderator names (moderatorList.json) and associated text (moderatorIntro* in groups.json) for displaying at the top of Tavern chat.

I'm not sure what you'll think of my decision to put the names in a file by themselves - I think it will be most convenient to avoid unnecessary Transifex changes when/if the names change, but I might be wrong. I can move the names into groups.json if desired.

See https://github.com/HabitRPG/habitrpg/pull/3661 for the jade file that uses this JSON data.