improved code styles #158 (#172)

* use php-cs-fixer instead of phpcodesniffer
* updated scrutinizer config
* adjusted code yules to all files
* updated CONTRIBUTING guidelines

src/Timesheet/CalculatorInterface.php

@@ -22,7 +22,6 @@ interface CalculatorInterface
      * The methods return value will not be evaluated.
      *
      * @param Timesheet $record
-     * @return void
      */
     public function calculate(Timesheet $record);
 }