Fixed up the density of the SPD services, SDD, and SSD cone material, and

Fixed up the density of the SPD services, SDD, and SSD cone material, and
repaired some related bugs. I have added a switch,
SetDensityServicesByThickness(), and SetDensityServicesByMass() which
toggle between two services thickness assumption, By default less aggressive
SetDensityServicesByThickness() is set. See
http://www.Physics.ohio-state.edu/~nilsen/ITS/ITS_MatBudget_4B.xls for the
calculation of the material budget used in this geometry. Comments in the
code also discribe these changes.