apply sensitivity to counter numbers when explicitly specified

Before this commit, number of calls to counters were not applied any sensitivity. This stays true by default, but when a sensitivity is defined explicitly for a given counter, it will now be applied also to the number of calls

The reason of being of this MR is the be able to move more easily to DD4hep. As a matter of fact this move exercises the Kalman filter instabilities and despite identical geometries (but last digit differences in the double numbers), we get different results after the Kalman fit than with DD4Hep. Moreover, these differences also impact the number of calls to the counters of the Kalman fit, as the convergence can be different. Hence the need to be able to put a sensibility also on nb of counter calls.