use dune-randomfield as random field generator
Ole wrote the dune-randomfield module on the same generator code base as DORiE's current generator. Switching to the other module should thus be relatively easy.
Things to note:
- the HDF5 files of dune-randomfield don't include attributes like grid extensions and probably have another HDF5 group structure. These things have to be added by the
doriePython wrapper after the RFG has written the data file.