Add "revoked" option to a Grant

[olmari]

We'd need revoke option in Grants (like there is in Tokens), instead of just plain deleting. Would make Vaasa hacklab door management more sane, as a member can be (too) late with monthly fees and thus have revoked door access, but after paid again, get access again.

I feel revoked option is more sane than to delete whole grant from that user in this case as deleting whole grant would also delete possible notes and so on, and also in more nitpicking, late with the monthly fees doesn't make door grant for a person "be gone" but exactly revoked.

Also we don't like to revoke a token itself in every situation, as they could still be used as utility tokens should member visit only at open house day.