The model can be used with either mole or mass fractions. The property

useMoles has to be set in the problem file and the boundary conditions 
have to be choosen accordingly.

In order to be consistent with the multicomponent models (3p3c,
3p3cni,...) the model uses MOLE fractions by default now.

The documentation is changed and extended accordingly.

reviewd by kathinka


git-svn-id: svn://svn.iws.uni-stuttgart.de/DUMUX/dumux/trunk@11525 2fb0f335-1f38-0410-981e-8018bf24f1b0