quadrature: Add `pfasst::augment_nodes` and handle `is_proper` flags appropriately.
imex: Support virtual nodes (0 and 1).
quadrature: Initialize matrix with zeros.
Style.
Merge remote-tracking branch 'memmett/feature/fix-quadrature' into development

* memmett/feature/fix-quadrature:
  Style.
  quadrature: Initialize matrix with zeros.
  imex: Support virtual nodes (0 and 1).
  quadrature: Add `pfasst::augment_nodes` and handle `is_proper` flags appropriately.

fixes PR #68

Signed-off-by: Torbjörn Klatt <t.klatt@fz-juelich.de>