[operators] removed common, eigen, istl
[operators.base] added to lib
[operators.affine] added to lib
[discretizations.interfaces] fixed get_vector_and_return_ptr()
[python-bindings] updated operator includes
[tests.operators] updated
[core.bindings] updated python bindings
[examples.stationarylinear] updated
[examples.stationarylinear] updated python bindings
[cmake] added typetree