[!!!][TASK] Deprecate IconUtility

Deprecate the IconUtility class from EXT:backend and handle its calls
using the new IconFactory from EXT:core.

Kudos to Benjamin Kott, Stephan Großberndt, Andreas Fernandez
and Frans Saris for the great support on this big project.

Resolves: #69057
Releases: master
Change-Id: I27a045b7a3b9d31e6e3e915e1452d44af56b0cee
Reviewed-on: http://review.typo3.org/42613


Reviewed-by: Andreas Fernandez <typo3@scripting-base.de>
Tested-by: Andreas Fernandez <typo3@scripting-base.de>
Reviewed-by: Benjamin Kott <info@bk2k.info>
Tested-by: Benjamin Kott <info@bk2k.info>
Reviewed-by: Stephan Großberndt <stephan@grossberndt.de>
Tested-by: Stephan Großberndt <stephan@grossberndt.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>