[TASK] Refactor Install Tool JavaScript

Resolves: #57182
Releases: 6.3
Change-Id: I2c8a7f594e3716152dfb9acb5246c741f7c9580d
Reviewed-on: http://review.typo3.org/28642
Reviewed-by: Susanne Moog <typo3@susannemoog.de>
Tested-by: Susanne Moog <typo3@susannemoog.de>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>