[bugfix] Make solverfactory tests work without optional pkgs

Closes #117

See merge request !570

Tests failed in Suitspares or UMFPACK was not there.

Fix some issues found by Clazy, Cppcheck, and myself

See merge request !569

Use the left-hand side as a condition

It was removed 9 years ago.

Remove `isPublic` altogether.
Found by Cppcheck (variableScope).

Found by Cppcheck (unusedVariable).

Found by Cppcheck.

This is less about performance and mor about silencing
the Clazy warnings.
Found by Clazy (range-loop-reference)

Cleanup the VariableBlockVector implementation

See merge request !463

fix bvector += bindings

See merge request !565

Set real_type of MultiTypeBlockVector

See merge request !480

Revert "Merge branch 'issue/block-traits-field-traits' into 'master'"

See merge request !567

This reverts merge request !564

Define BlockTraits in terms of FieldTraits

See merge request !564

refactor blockvector bindings to allow for generic types

See merge request !562

Add a specialization of FieldTraits for VariableBlockVector

See merge request !563

[cleanup] Remove unused allocators

See merge request !560

Remove allocator template parameter from the classes
`base_array_unmanaged`, `compressed_base_array_unmanaged`,
`block_vector_unmanaged`, `compressed_block_vector_unmanaged`, and
`CompressedBlockVectorWindow`.
All of these classes do not manage memory on their own.
The provided allocator was only used to deduce `size_type`.
The latter is now provided as template parameter explicitely.

Notice that this (seemigly breaking) change is safe, because
all these classes are clearly marked as implementation details
that should not be used outside of dune-istl.

Export missing functionality in MatrixIndexSet

See merge request !559

The `MatrixIndexSet` class provides access to an
incomplete subset of its internal data. While
the number of rows is exported, the number of cols
and the column indices per row have been missing
so far. This was an oversight, since one can hardly
use the class without this, unless one relies on
the dedicated `exportIdx()` method for `BCRSMatrix`.

With the missing data exported, one can now easily
use `MatrixIndexSet` to build patterns for
other sparse matrix classes.

Various fixes and tests for the printSparseMatrix method

See merge request !558

No fixes necessary.