Forward publish/set publish date

[HeyJoel]

This applies to pages and custom entities. Users should be able to set a publish date, which could be in the past or future. An example is a blog post that you may want to schedule to go live at a later date. You may also wish to edit a blog post that has already been published but the public 'publish date' should not change - you could set a property model for the 'display publish date' but you'd still need to have it ordered using the original publish date.

[HeyJoel]

The plumbing for this has been added in 0.2 but we still need to have an interface in the admin UI so you can set the date when you publish. Need to bear in mind the local time offset when capturing this information.

[HeyJoel]

Perhaps it would be useful for this to be a date range? Campaign pages may need to be unpublished at a certain date. Need to investigate.