Add atom types for He, Ne, Cl, and Ar

- this prevents receiving noce instead of atomType
- lateron it will could useful to distinguish ions
Use RDKit to generate geometries foe tri-valent nitrogen

- relax limitation on all nitrogen to penta-valent only, that way we can
make use of RDKit's advantages for cyclic compunds with tri-valent
nitrogen
- openBabel will now only be use for penta-valent nitrogen species
- improving the handling of the carbon monoxide exception introduced in
c7ca1ba0c02f29eb65d32068dc4d02dc56febd89 because it could lead in some
cases to wrong drawings by confusing the order of the atom labels during
rendering