[FEATURE] Introduce new Icon API

The logic for working with icons, icon sizes and icon overlays is now bundled into the new IconFactory class.
The new IconFactory will replace the old icon skinning API step by step.

All core icons will be registered directly in the IconRegistry class, third
party extensions must use IconRegistry::registerIcon() to overwrite existing
icons or add additional icons to the IconFactory.

The IconFactory takes care of the correct icon and overlay sizes and the markup.

Resolves: #68741
Releases: master
Change-Id: I731e077290b58298c2c603eeb8961e8a3d4c62d3
Reviewed-on: http://review.typo3.org/41759


Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>