Remove dependency on redis / kredis for sudoable

[javierav]

The dependency on kredis can be eliminated by persisting the information in the database.

[lazaronixon]

Hey, well done. I particularly dislike sudo_at > 30 minutes ago, but since we're removing a dependency and it's the only place we're using kredis, it's worth it.

[javierav]

@lazaronixon an alternative may be

(30.minutes.ago..).cover?(sudo_at)

But I think is more complicated...