adopt block number revocation status instead of boolean verdict

[mirceanis]

Revocation status is being returned as an object of the form:

{
  revoked: true
}

To make use of the latest contract improvements, this status should return the lowest block number when a valid revoker issued a revocation, or 0 if it was never revoked by any valid revoker address(es).

Ex:

{
   revoked: 19265
}

With a status like this, integrators ca query the block timestamp to figure out when the credential was first revoked.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.