[TASK] Replace gfx/content_client.gif with sprite icon

Resolves: #68019
Releases: master
Change-Id: I0236b5a477f2a74d111571f5bafb05f8d28b3e68
Reviewed-on: http://review.typo3.org/41061


Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Stephan Großberndt <stephan@grossberndt.de>
Reviewed-by: Markus Klein <markus.klein@typo3.org>
Tested-by: Markus Klein <markus.klein@typo3.org>