merge from implicit branch: deprecate BoxDarcyFluxVariables in favor of

ImplicitDarcyFluxVariables. Adapts includes and setting of properties.
fix Forchheimer flux variables. get rid of the extra
elementIntrinsicPermeability function again, at the expense of more
complicated code in the flux variables. Works now for both scalar and
tensorial perms. deprecate BoxForchheimerFluxVariables in favor of
ImplicitForchheimerFluxVariables. Adapts includes and setting of
properties. Reviewed by gruenich.


git-svn-id: svn://svn.iws.uni-stuttgart.de/DUMUX/dumux/trunk@9864 2fb0f335-1f38-0410-981e-8018bf24f1b0