Implementation of array jobs

Small improvement over merge request #12 

Finally enable submitting array jobs via the ```submitArrayJob``` method of ```Batchelor```. This method calls the ```submitJob``` function of the underlying implementation, for the moment this can be done at E18, GridKA and Lxplus. ```getListOfActiveJobs``` was adjusted to return a list of tuples containing the job and task IDs (and the status), ```submitJob``` continues to return only the job ID.

Possible issues:
* Tasks at Lxplus mean something entirely different from what they mean at E18 or GridKA.
Setting arrayStep = 1 might be a sensible default.