05-03-04 Gas Flux model update

Change with respect to the NC_GasFlux model.

Introduced new function for the exchange between the anaerobic balloon and the aerobic site in the air pore volume. The previous function was only governed by one parameter IntDiffRedFrac which caused an optimom exchange at 50 % anarabic fraction and with zero exchange both att 100 % and 0 %. The new parameter will add a base level by the value of IntDiffRedFracBase to the previous function.  PEJ/JN