Add unarchiving task


(https://cloud.githubusercontent.com/assets/93511/5201656/12bc7c8c-756d-11e4-91ff-fb817ab01e4e.png)
https://www.agileplannerapp.com/boards/173808/cards/8018

Provides a simple way to 'unarchive' Editions by creating a draft version and force publishing it.
See discussion here https://www.agileplannerapp.com/boards/173808/discussions/2428 for more background.

![screenshot - 261114 - 13 06 14](https://cloud.githubusercontent.com/assets/93511/5201674/43635c52-756d-11e4-85a4-515e426b8237.png)