Molsystem

* Enhanced the OpenBabel molecule interface to handle periodic systems better, which
in turn supports using SDF files for periodic systems using SEAMM-specific
customization. The coordinates are always stored as Cartesians, and the cell
information is added as a property, and used when reading periodic systems written
by SEAMM.
* Added code to the RDKit interface to allow setting/getting just the coordinates
to/from a RDKit Molecule object. This is in analogy to the implementation in
OpenBabel.
* Added code to truncate near zero coordinates and cell parameters (< 1.0e-6) to make
coordinates and the cell parameters easier to read.

* This fixes an error in toRDKMol and toOBMol when the system or configuration name
is None.

* Generalized the alignment/RMSD code to make it easier to do berofe and after
comparisons in optimizations and similar applications.
* Fixed a bug in the handling of spacegroup names. The full inetrnational symbols
with added setting information were not properly recognized.

* Fixed bug in isomeric SMILES and generally improved the handling of SMILES using
RDKit.
* Improved error checking for types when saving properties to the database.
* Added control of properties when going to/from RDKit and OpenBabel.

* JSON properties were read as strings, not as JSON objects. This is fixed.

* The full precision coordinates are added as a property to the SDF file. If the
full-precision coordinates are aavailable they are used when reading the SDF file.