LArCalib RTM-Parameter extraction job: Allow to process channels with tbb::parallel_for

The RTM-Parameter job is the only job of the LAr Electronic calibration procedure that is truly CPU-bound and fairly slow (about 3h) in walltime. The same calculation is performed for each calorimeter channel independenlty, so the task can be easily parallelized.

Note that all the caluclation are done in stop(), the job as no event loop.