v4.0.0

Changelog for 4.0:

Breaking changes

• All service defintions now use class names instead of old-styled names. You might have to change your Dependency Injection if you inject CmsBundle's services by their name.
• Added default validation constraints for Page and Category entities. This might break your app if you pass Page or Category entities through Symfony Forms.
• Removed Category::$createdAt, didn't really make sense.
• Replaced DateTime with DateTimeImmutable in the Page entity.

Other changes:

• Symfony 5.0 is now required
• PHP 7.3+ is required
• Added a PostsController to use Page objects like blog posts with date in URL (#25)
• Use Symfony/String instead of Behat/Transliterator as a slugger
• Made setters accept null as argument, for flexibility with how the Form component usually works