Computes saturations based on depths
    For constant capillar pressure function the saturation is
    determined by cell depths:

    Sg_max, Sw_min
    ----- goc ----
    Sg_min, Sw_min
    ----- woc ----
    Sg_min, Sw_max
    Implements initialization for constant capillary pressure functions
Merge pull request #628 from totto82/constCapPressInit2

Initialization for constant capillary pressure functions