Add profile suspension mode

[sebgrebe]

Current state

• Users can be either approved or not
• To suspend a user, we currently unapprove them
• By default, newly created users are unapproved
• This can create confusion: is a user unapproved because they were just created or because they were suspended? Admins might approve a suspended user because they think the user is newly created

Acceptance criteria

• Add profile field "suspended"
• Default is false, but make sure suspended users will be set to true (sebgrebe and vagarwalla know who these are)
• Add admin action for suspension
• Remove "unapprove" action on admin panel
• Add suspension column to admin panel
• If a user is suspended, they are automatically unapproved