Add driver that performs SVT cluster position smearing

[bloodyyugo]

Add a driver to be used (optionally) to smear the local SVT cluster positions in MC.

The goal is to better duplicate the hit residuals and track chi2 seen data but the plan is to start simple and add complexity.

• step 0: single smearing factor (or absolute number) for all clusters over all layers and nHits
• step 1: separate factors for 1 & 2 hit clusters
• step 2: also separate by layers in some way (eg L0+L1 vs the rest or L0+L1, L2+L3, outer layers)
• step 3: position dependent smearing ... we would need some guidance from data for this

I don't plan to include everything in this issue, probably just up to step 2.

[bloodyyugo]

It would be even better to move the smearing down to the SVT hit making level, based on some real physical basis. TKNelson has some experience with tuning MC in this way, so he will consult on that. Plan for that to be next project after this.