Add unarchiving task

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.
This will never fire because if the `find` on line 5 fails, it will raise an exception there.