Remove pybind11 from 3rd Party packages

I propose to remove pybind11 from the 3rdParty packages and instead have the user install it (which can be done via pip or conda). That way fewer external libraries have to be shipped together with VF and it is easier for users to update the version (there were some issues recently with a combination of an old pybind and a new python). Pybind11 can be included through the cmake find-package mechanism. Alternatively, we can ship a "backup" pybind11 but only include it if cmake cannot find an installed pybind.