replaced the boundary condition functions with the respective "atPos"
functions (Dumux day task)
introduced a "atPos" function for the Beavers-Jospeh Coefficient
applied naming convention to the bBox variables

reviewed by gruenich



git-svn-id: svn://svn.iws.uni-stuttgart.de/DUMUX/dumux/trunk@14096 2fb0f335-1f38-0410-981e-8018bf24f1b0