Let's adhere to styleguide

using `and` in an expression can sometimes
lead to unexpected behaviour. best used only
for flow control. see:

https://www.tinfoilsecurity.com/blog/ruby-demystified-and-vs
Editions can be scheduled for publishing
Allow scheduled publishing to be cancelled
Split scheduled publishing tests out
Added schedule for publishing to actor
Editions scheduled for publishing can't be edited

... and making the method used for validation private
as it is not being used outside. conveys intent clearly.
Editions scheduled for publishing, can't destroy
Dynamically define scopes based on states

needed to define one for scheduled_for_publishing,
ended up doing this.
Adding status_text to accomodate more details
Add cancel scheduled publishing workflow action
Transtion to published state from scheduled
Reloading to ensure edition was persisted
Merge pull request #129 from alphagov/implement-scheduled-publishing

Implement scheduled publishing