[CLEANUP] Code cleanup EXT:filelist

Refactor the code to go green in PHPStorm.
Main tasks:
* Initialize variables
* Centralize objects in $GLOBALS

Resolves: #64496
Releases: master
Change-Id: I3c5803e818bb7f5b1fded7935b4590e4aaf312f6
Reviewed-on: http://review.typo3.org/36279


Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Philipp Gampe <philipp.gampe@typo3.org>
Tested-by: Philipp Gampe <philipp.gampe@typo3.org>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>