Fix date formatting and event handling.

There were a number of issues with the way `published_at` was handled:

 * 'Not Published' was never shown
 * JS Errors when `published_at` was never set (pubDate === null -> pubDate.isSame)
 * Setting the date manually makes it appear falsely formatted (13 Oct 13 comes up as 12 Jan 10, parseDateFormats didn't work because `published_at` is stored as DateTime in the database).