[TASK] Some code cleanups

* Removes "invalid password" image and use the yellow
one from TYPO3 Core
* Refactored PasswordEvaluator

Releases: 6-2
Change-Id: Ide29e558538b505f05b7c17d5a5be9a2005b5aad
Reviewed-on: https://review.typo3.org/25064
Reviewed-by: Thomas Loeffler
Tested-by: Thomas Loeffler