Saturation table scaling and hysteresis.

This commit implements some additional scaling keywords.  This includes
the ISWL-family that provides hysteresis behavior via alternative
scaling of the tables.  The old parser has been somewhat extended for
testing purposes.  The commit also includes a slight re-factoring of the
SatFunc-family where a new base class has been introduced.

Note:
- The scaling and hysteresis behavior is implemented by overloading member functions of the SatFunc-classes, and the original functions are supposed to work exactly as before.  The overloaded interface is completely implemented for SatFuncGwseg but not for SatFuncSimple and SatFuncStone2.
- For hysteresis to work as intended, the method SaturationPropsFromDeck<SatFuncSet>::updateSatHyst(...) must be called for each completed time-step.  This call is not included in the current commit.
- The re-factoring of the SatFunc-family, has currently made SatFuncGwseg.cpp and SatFuncStone2.cpp superfluous and the current SatFuncSimple.cpp should probably change name to SatFuncBase.cpp