[BUGFIX] feedit: Use skinImage for edit icons

Replace hardcoded icons with t3lib_iconWorks::skinImage calls

Change-Id: I02236b36facb53222ccc8e0bfc17adf7b2ac7ae4
Resolves: #24920
Releases: 4.5, 4.6
Reviewed-on: http://review.typo3.org/3448
Reviewed-by: Steffen Kamper
Tested-by: Steffen Kamper
Reviewed-by: Stefan Neufeind
Reviewed-by: Susanne Moog
Tested-by: Susanne Moog