Added charge correlation between cathods.

Added charge correlation between cathods.
In Config_slat.C, use
 MUON->Chamber(chamber-1).SetChargeCorrel(0.11); to set the RMS of
 q1/q2 to 11 % (number from Alberto)
 This is stored in AliMUONChamber fChargeCorrel member.
 At generation time, when a tracks enters the volume,
 AliMUONv1::StepManager calls
 AliMUONChamber::ChargeCorrelationInit() to set the current value of
 fCurrentCorrel which is then used at Disintegration level to scale
 appropriately the PadHit charges.