Feature/istl solver factory

Add Istl solver factory backend originally implemented by @msblatt

• Depends on MR 349 in dune-istl (merged)

• Depends on !1848 (merged)

• Supersedes !1839 (closed) and !1841 (closed).

• Fixes #810 (closed)

• Fixes #652 (closed)

TODO:

• Rebase if !1850 (merged) is merged and adapt structure to new parallel solver internal structure
• Fix template parameter -> only: <LinearSolverTraits>. Depends on fix for #805 (closed) (see !1850 (merged))
• Deprecate old preconditioner params (without subgroup)? -> to be fixed for #825 (closed)
• Add unit test for the linear solver -> base on dune-istl test as suggested in !1850 (merged)

Notes to the reviewer Test with dune master (uses solver factory) and dune 2.7 (uses amg). Only need to test test_richards_lens_*, test_shallowwater_dambreak and test_linearsolver