Add test of inverse action-angle isochrone for non-inclined and almost non-inclined orbits (fails until before the next commit, because the longitude of the ascending node is not well-defined)
Add test of inverse action-angle isochrone for non-inclined and almost non-inclined orbits (fails until before the next commit, because the longitude of the ascending node is not well-defined)

jobovy/galpy,jobovy/galpy,jobovy/galpy,jobovy/galpy