Cookiecutter for sample_restraint
Since the gmxapi sample_restraint code is now a subproject of the
GROMACS project, it is no longer trivial to fork a new MD plugin
project.
A reasonable solution could be a skeletal Cookiecutter repository that
draws the sample_restraint subtree from the GROMACS repository. We
could also separate some of the CMake logic, in that case, to better
handle bundling of pytest, googletest, and testing infrastructure set-up.