Add an improvement to workflow to allow multiple users to approve an issue in any order

A customer has requested that an issue could be approved by mutiple users in a non-linear fashion, but still ensuring that those designated users would all still have to approve the issue before it could change its status to approved.

e.g. an issue is assigned for approval by a certain group. Each member of that group is alerted to the fact that an issue is awaiting their approval and the issue is not approved until all members of that group have approved the issue. Any member of the group can approve the issue at any time and there is no set order.