* Don't change published_at for articles that have already been published (even if unpublished later)
* Removed unused code related to changing published_at
* Added specs for updating published_from_feed articles, fixed specs
* Removed old validation
* Added specs for article validation published_from_feed
* Added and reorganized specs for the Article model (setting published_at)
* Remove the commented code, added a spec
* Added specs for unpublishing
* Removed unused update_published_at from article attributes spec
* Fixed nullifying published_at seconds when republishing from rich editor
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