Add ability to track admin canceler

This PR adds the ability to track the admin user who canceled an order. The information is displayed in the order summary left side below the approver information. Nil checks were taken as a precaution (perhaps un-necessarily?) when the cancelation is done outside of admin and the order is canceled but no admin did it.

![screen shot 2014-10-08 at 10 36 10 am](https://cloud.githubusercontent.com/assets/134368/4560904/9963be30-4ef8-11e4-849f-f00a22485664.png)