Fixing the calculation of the cross talk in the Micromegas digitization

This MR fixes the simulation of the cross talk. Now the charge on the central strip is scaled down by the amount of cross talk to the neighboring strips. Before the amount of shared charge was determined on the full charge and subtracted from the central strip, leading to unrealistic charge ratios and negative charges on the central strip.

Adding urgent since new samples with this MR need to be created quickly