Sitemap Plugin Versions Save

Check the the upgrade guide to see how to upgrade. A lot has changed. Major changes:

• Generating the sitemap is not done on the fly anymore, but from the CLI.
• Upgraded to PHP ^7.4
• Overall refactor (including BC)

• Added Sylius Coding Standards including ECS
• Upgraded PHPStan version and moved away from SHIM version
• Allowed wider dependencies for multiple dev dependencies (e.g. PHPSpec & PHPUnit)
• Added strict typing
• Run Travis against PHP 7.3

Although strict typing is a big change, it should not impose any breaking changes.