Ref T12313. This puts a UI on revoking credentials after a widespread compromise like Cloudbleed or a local one like copy/pasting a token into public chat.

For now, I'm only providing a revoker for conduit tokens since that's the immediate use case.

• Revoked in user + type, everything + user, everywhere + type, and everything + everywhere modes.
• Verified that conduit tokens were destroyed in all cases.