-Removed not working and unused numericalDensity

-Introduced FluxData for compositional models, only storing upwind information
-Transport can use full upwind or harmonic average if upwind direction changes from P.E. (settable via property RestrictFluxInTransport)
=>reduces effect of flow that is not accounted for in the P.E.
reviewd by Philipp

git-svn-id: svn://svn.iws.uni-stuttgart.de/DUMUX/dumux/trunk@8094 2fb0f335-1f38-0410-981e-8018bf24f1b0