simplify and cleanup the SolverFactory

See merge request !453

getMatOrThrow handed out a reference to the underlying matrix, but for
the compiler it was undecidable, whether this might be a dangling
refernce. This lead to many warnings. We now hand out the
AssebledLinearOperator and call getmat explicitly where ever needed.

In the rewrite the vector types of UMPack were checked, similar to the
other direct solvers. This does not work anymore, as recent changes in
UMFPack now lead to a compiler error if the vectors are not available,
i.e. when using a real-type different from double. This change now
(re-)introduces a SFINAE check to ensure that the types are compatible.

cleanup a range of warnings

See merge request !583

Catch polymorphic type ISTLError by reference

See merge request !581

Found by GCC (Wcatch-value)

Update changelog release 2 10

See merge request !576

Update versions release 2 10

See merge request !575

Improve UMFPack vector chooser

See merge request !546

Fix misc warnings

See merge request !574

* Assign unused arguments to std::ignore to avoid warnings

Fix more Cppcheck findings

See merge request !571

Found by Cppcheck (unreadVariable).

Found by Cppcheck (unreadVariable).

Found by Cppcheck uselessOverride).

Avoid unwanted copies of the iterator.
Found by Cppcheck (postfixOperator).

Found by Cppcheck (missingInclude).

Update LICENSE.md

See merge request !573