Faults: Calculate riMULT average cell face multiplicator

[hhgs]

Calculate average cell face multiplicator for X, Y and Z, including both Neighbor cell transmissibility and Non-Neighbor Connection transmissibility for a given cell face.

Cell faces with no overlapping surface area to other active cells should be given "nan", in order to separate them from cells faces where flow can occur and where multiplicators = 1.

[hhgs]

Parameter name example: riMULTXmean
For cells without any overlapping area, use 'nan'.