Check for published status on save.
Check for published status on save.

If the article is published but no published_at date exists, set it
before saving the model.

If the article is set to draft but has a published_at date, set the
published_at date to null.

Signed-off-by: Spencer Deinum <505277fcd2f4c2913fe2f569996e74d8e809c2be@gmail.com>

laraveltokyo/laravel-forums,luckys/laravel.io,andela-cijeomah/laravel.io,laraveltokyo/laravel-forums,barryvdh/laravel.io,philip8728/laravel.io,janusnic/laravel.io,carlogaza/laravel.io,liduanw/laravel.io,dinorastoder/laravel-io-development,andela-cijeomah/laravel.io,chirilo/laravel.io,dprevite/laravel.io,RyansForks/laravel.io,dprevite/laravel.io,pedrofornaza/laravel.io,chirilo/laravel.io,LaravelIO/laravel.io,irfanevrens/laravel.io,luckys/laravel.io,RyansForks/laravel.io,masterpowers/laravel.io,SaifulAzam/laravel.io,LaravelIO/laravel.io,laravelbrasil/laravel.io,yccphp/laravel.io,andela-cijeomah/laravel.io,janusnic/laravel.io,MehmetNuri/laravel.io,dinorastoder/laravel-io-development,chirilo/laravel.io,ShawnMcCool/old-lio,yccphp/laravel.io,pedrofornaza/laravel.io,MehmetNuri/laravel.io,liduanw/laravel.io,Stanvk/laravel.io,barryvdh/laravel.io,ShawnMcCool/old-lio,pedrofornaza/laravel.io,masterpowers/laravel.io,LaravelPeru/laravel.io,MehmetNuri/laravel.io,laraveltokyo/laravel-forums,dinorastoder/laravel-io-development,carlogaza/laravel.io,yccphp/laravel.io,laravelio/portal,luckys/laravel.io,janusnic/laravel.io,ShawnMcCool/old-lio,dprevite/laravel.io,Stanvk/laravel.io,janusnic/laravel.io,janusnic/laravel.io,LaravelPeru/laravel.io,laravelbrasil/laravel.io,irfanevrens/laravel.io,SaifulAzam/laravel.io,masterpowers/laravel.io,Stanvk/laravel.io,jew977/laravel.io,philip8728/laravel.io,barryvdh/laravel.io,laravelbrasil/laravel.io,laraveltokyo/laravel-forums,LaravelIO/laravel.io,SaifulAzam/laravel.io,barryvdh/laravel.io,RyansForks/laravel.io,laravelio/portal,RyansForks/laravel.io,LaravelPeru/laravel.io,liduanw/laravel.io,laravelbrasil/laravel.io,philip8728/laravel.io,laraveltokyo/laravel-forums,laravelbrasil/laravel.io,jew977/laravel.io,laravelio/portal,barryvdh/laravel.io,irfanevrens/laravel.io,carlogaza/laravel.io,jew977/laravel.io,dinorastoder/laravel-io-development,ShawnMcCool/old-lio