Feature Request - Allow users to schedule publication of Pages & Posts

[patricklindsay]

As a user I would like to be able to set a specific time and date for a page or post to be published.

Implementation Idea

• Add a scheduled status
• Add scheduled_at date time
• Allow users to set to scheduled when status is draft
• When selecting scheduled status input should appear allowing user to set scheduled_at datetime (time granularity should be every 30 minutes)
• Create rake task which publishes all instances with status equal to scheduled and scheduled_at in the past.

As part of ENV setup developer has to setup a CRON job to run the rake task every 30 minutes or so (can do this with Heroku using the Scheduler addon).