Various improvements for dune-fem.
This merge request is a rebased/squashed version of the feature/codegen branch. It contains changes regarding quadrature keys, improved codegen features and a revision of the linear solvers plus various bug fixes.
This merge request is a rebased/squashed version of the feature/codegen branch. It contains changes regarding quadrature keys, improved codegen features and a revision of the linear solvers plus various bug fixes.