Add Static Code Analyzer

[alexander-schranz]

The following Static Code Analyzer should be added to the Code Base

• https://github.com/phpstan/phpstan
• https://github.com/PHP-CS-Fixer/PHP-CS-Fixer
• https://github.com/maglnet/ComposerRequireChecker
• https://github.com/Roave/BackwardCompatibilityCheck