[TASK] Deprecate IconUtility::getIcon and clean up "gfx/i/"

[TASK] Deprecate IconUtility::getIcon and clean up "gfx/i/"

The method IconUtility::getIcon was used for returning
overlaid icons before TYPO3 CMS 4.4, based on raw icons
inside gfx/i/ and created temporary icons when not present.

The left-over function calls are replaced with sprite icon calls.

Additionally, in order to thin out typo3/gfx/, all icons which have
always been overlaid with t3skin already have been removed. All
other files from typo3/gfx/i/ are moved to EXT:t3skin to
stay compatible.

With TYPO3 CMS 8, the folder EXT:t3skin/icons/gfx/i/ will
be completely removed with the function itself.

Resolves: #67506
Releases: master
Change-Id: Idc20fadd36ffeb26782d8d54e27802a0412f9516
Reviewed-on: http://review.typo3.org/40305
Reviewed-by: Jan Helke <typo3@helke.de>
Tested-by: Jan Helke <typo3@helke.de>
Reviewed-by: Frederic Gaus <frederic.gaus@flagbit.de>
Tested-by: Frederic Gaus <frederic.gaus@flagbit.de>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>