use config to import concrete class, we have to discuss how to address the different number of parameters given to our constructors.
tried to reorganize the worker... this is more a idea then a concrete solution, still not happy with it.
reorganization of worker, still not happy with it but a good starting point i guess.
as long as we do not have tests and tester is used, make the worker backend configurable.
Merge pull request #4 from BeneDicere/master

modification of imports, reorganization of workers