[TASK] Code cleanup: ColorpickerController.php

backend/classes/Controller/Wizard/ColorpickerController.php
To get it "green" in PhpStorm several changes were made:

- set correct return type in PhpDoc comment
- makeInstance of GraphicalFunctions to call non-static function
  imageCreateFromFile
- change local variable names to lowerCamelCase

Resolves: #65431
Releases: master
Change-Id: I54182c8ed17423e1cbc1c97e424d92a58dd5e3a9
Reviewed-on: http://review.typo3.org/37404


Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>