Choosing which parametrization is used for the Nusselt / Sherwood correlation:

Introducing a new property:
NusseltFormulation
SherwoodFormulation

Defining possible values in dimensionlessnumbers

The actual call to the function now additionally needs a flag for which formulation to choose. 

add a bunch of consts in order not to accidentially change parameteres (mpncvoluemvariablesiakinetic)

reviewed by Bernd

git-svn-id: svn://svn.iws.uni-stuttgart.de/DUMUX/dumux/trunk@11504 2fb0f335-1f38-0410-981e-8018bf24f1b0