[BUGFIX] Fix missing method getCategories

Change-Id: Ide6f0eff6f8c4559dadc407ea63c3f57ce809e88
Releases: 3.0
Resolves: #61018
Reviewed-on: http://review.typo3.org/32214
Reviewed-by: Fabien Udriot <fabien.udriot@ecodev.ch>
Tested-by: Fabien Udriot <fabien.udriot@ecodev.ch>