Enable other moderators

[aluhrs13]

P0:

• [x] Remove emails when the user is a moderator and not an admin
• [x] Make sure UserManager is admin only

P1:

• [ ] Document every moderator page
• [ ] Document TagPair workflows

P2:

• [ ] Approving a tag from the pending tags page shows an error (but succeeds)
• [ ] Fix CreatorManager page
• [ ] Should TagPairManager even work?