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.

reviewed by kathinka


git-svn-id: svn://svn.iws.uni-stuttgart.de/DUMUX/dumux/trunk@11527 2fb0f335-1f38-0410-981e-8018bf24f1b0