Scifi noise improvements

Improved the simulation of noise (thermal noise, direct and delayed cross talk, afterpulses) in the SciFi digitisation. Before, the simulation of thermal noise was taking a lot of time in Boole, because it was creating many (300k) low-charge MCFTDeposits that did not make the clustering threshold. Now, an effective noise simulation has been implemented. These changes speed up the SciFi digitisation by about 30% (about 0.35 second). The number of clusters stays the same. More information can be found in these presentations in the SciFi simulation meetings:

• https://indico.cern.ch/event/644852/ (Jun 7)
• https://indico.cern.ch/event/651523/ (Jul 5).

For the thermal noise generation, one can switch back to the old behaviour with: MCFTDepositCreator().FTNoiseTool.SimulateEffectiveNoise = False The simulation of delayed cross talk is completely new. In addition, the expected noise levels are updated with the latest information from https://cds.cern.ch/record/2259100/files/LHCb-INT-2017-006.pdf.

The effect on the tracking is also checked (see agenda Jul 5). The number of ghost tracks is (almost) identical for the effective and detailed thermal noise simulation (even for 2x the expected noise level = 28 MHz).

This MR closes LHCBSCIFI-81, closes LHCBSCIFI-2 and close LHCBSCIFI-82.