WIP: Fix of the surfaces in MM readout elements and on MM clusters uncertainties.
This MR should fix a series of problems observed in the MM tracking residuals, that appear when using cluster uncertainties corresponding to the real uncertainties.
First problem concerns the position of the surfaces in the MMReadoutElement: the surfaces were moved to the position of the readout strips ( with a bug in this movement, in any case ), while they should remain at the center (along global Z) of each gas gap.
This has implications on MM digitization: the new position of the MMReadoutElement surfaces should be taken into account.
Another problem is observed in the stereo layers: clusters are associated with very low efficiency.