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: Ibef1d71f1d3a6aa3683331464b33118b88b1ec01
Reviewed-on: http://review.typo3.org/16329
Reviewed-by: Steffen Ritter
Reviewed-by: Helmut Hummel
Tested-by: Helmut Hummel