use OPM instead of dune infrastructure wherever possible

basically the only Dune thing which is still used are the FieldVector
and FieldMatrix classes used by some constraint solvers. Until
something similar goes into opm-core, opm-material must depend on
dune-common...
remove the dependency on dune-istl from dune.module

the only reason dune-istl was required was that the spline class used
ISTL's tridiagonal matrix. Since the spline class moved into the core
(along with a more capable tridiagonal matrix), ISTL is no longer
required by opm-material.
remove the dune-istl from the list of prerequisites

the only reason dune-istl was required was that the spline class used
ISTL's tridiagonal matrix. Since the spline class moved into the core
(along with a more capable tridiagonal matrix), ISTL is no longer
required by opm-material.
Merge pull request #13 from andlaus/reduce_reliance_on_dune

Discussed with Atgeirr