Copies and different orders in std::set

[sjunges]

We bind quite some vectors and sets, which are currently copied explicitly every time, see https://pybind11.readthedocs.io/en/stable/advanced/cast/stl.html.

It may be good to think about this.

Another problem is that for sets, the c++ version and the python version of sets are ordered differently, and that in particular python sets are not ordered consistently between different runs.