Provide a reason why you are deleting a work

Hello,

This will record a user provided delete reason in the work's internal comments attribute.

It deletes by calling the AmberDB `deleteWork` method.

Huw

![screen shot 2014-04-30 at 12 32 39](https://cloud.githubusercontent.com/assets/790199/2837143/bb2bfd88-d00f-11e3-8f97-7b6be00255a2.png)