Replace calls to deprecated `DUNE_VERSION_NEWER_REV(DUNE_ISTL,2,7,1)`
by `DUNE_VERSION_GT_REV(DUNE_ISTL,2,7,0)` which also reads better than
the `GTE` version, as Dune 2.7.1 hasn't been released yet. Fix the
call to `DUNE_VERSION_GT(DUNE_ISTL,2,7)` in the solver factory
backend which would break things in case of a 2.7.1 release. Adapt
the corresponding changelog entry.

* throw exception when used in parallel because this feature
is only available for >= 2.7.1

Kilian Weishaupt authored Mar 17, 2020 and Kilian Weishaupt committed Apr 07, 2020

* check matrix type, chose appropriate function (dune or dumux)
* MultiTypeBlock matrix only works sequnetially so far

We do not need to support the old style parameters as this class was
just recently added on master.

Backwards-compatible implementation. Legacy parameter names
e.g. PreconditionerIterations will still work but subgroup params
overwrite them, e.g. Preconditioner.Iterations.

Markus Blatt authored Jan 26, 2020 and Timo Koch committed Mar 11, 2020

This requires a version newer than 2.7.0. The backend translates
the configuration parameters from Dumux CamelCase to the dune-istl
names. If a Dumux parameter is not found we fall back to using
the dune-istl parameter name.

We fall back to the parallel AMG backend if the DUNE version is
not sufficient.