All abstract classes should be start with an Abstract
prefix in the class name.
Adjust the abstract task class to this naming convention.

Resolves: #42803
Releases: 6.0

Change-Id: If0b62d4ff61d9aa7ce44f61a15457faeabeab2d7
Reviewed-on: http://review.typo3.org/16331
Reviewed-by: Helmut Hummel
Tested-by: Helmut Hummel