[operator.oswald] added first draft * added OswaldInterpolation from elliptic estimator test, seems to work   but is untested and inefficient * added first draft of OswaldInterpolationLocalizable, does not work yet
[operator.oswald] added first draft
* added OswaldInterpolation from elliptic estimator test, seems to work
  but is untested and inefficient
* added first draft of OswaldInterpolationLocalizable, does not work yet

pymor/dune-gdt