[!349] Metadata options

Merge branch 'feature/metadata-options' into 'master'

ref:extensions/dune-codegen Some options are well suited to be set from the
metadata dictionary of UFL measures. This MR implements the necessary
infrastructure. While at it, it solves some more issues with options.

This fixes [#148]

See merge request [extensions/dune-codegen!349]

  [#148]: gitlab.dune-project.org/NoneNone/issues/148
  [extensions/dune-codegen!349]: gitlab.dune-project.org/extensions/dune-codegen/merge_requests/349


Closes #148