Implement grid property initializers

this makes it possible to use basically arbitrarily complex initialization schemes for grid properties. The second patch uses the new infrastructure for the endpoint scaling keywords where the defaults are given by  lookups in the SWOF/SGOF tables. @osae: could you please check that the correct default values are used before this is merged?

On an unrelated issue, I noticed that we will probably need to introduce a "grid property post-processors" to be fully spec compatible because for e.g. PERM[XYZ] the spec says that only the top layer of cells needs to specified and if the remainder is left undefined, the values should be copied from the topmost layer. This behavior cannot be implemented at the moment.. (Not that any sensible deck would ever want to do such a thing, but it is in the spec...)
Here you should subtract "connate gas", even if that one is usually zero anyway:
criticalOilOGSat[tableIdx] = 1 - Sw - minGasSat[tableIdx];