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.
To get an audit entry, it might be an idea to perform this in an audit trail block:

```ruby
Edition::AuditTrail.acting_as(user) do
  EditionForcePublisher.new(draft).perform!
end
```