Fixed some scrutinizer issues

[garrettw]

• corrected bug in almost-duplicate code in Pimf\Controller\Core
• added missing @property doc for REDIRECT_URL in Pimf\Environment
• corrected parameter type in docblock for Pimf\Session\Payload::$session
• consolidated duplicate code in Pimf\Util\Header

[gjerokrsteski]

@garrettw thank you for the fixes. The ci pipeline is fine. The php5.6 and php7 pipelines are failing, but that is only a code-coverage ;-)