ViennaMaterials API changes-induced update

-> the device class generates the ViennaMaterials path accessors
-> device methods and problem methods access these via the device class
-> ViennaMini is now decoupled from the material library backend
fighting with SRH terms in the n/p equations - removed from examples

SRH terms work if it is exactly the same integrated like in the nin1d example.
however, as soon as quantities are introduced, it stops working.
need to investigate, whether some uninitialized quantities introduce
errors here (maybe it is not a ViennaFVM problem at all ..)