Added equality and inequality operators for atoms and bonds

Simple tests verify the functionality, and provide for easy comparison
of atoms and bonds.

Change-Id: Icb25f45668d52e8983ab19fe832d55b9732ab800
Extended the unique id foundations in Molecule

Atom and bond unique IDs now have additional API allowing you to obtain
unique IDs for atoms and bonds, obtain the corresponding atom or bond
and restore unique IDs that were previously removed from the molecule.

Change-Id: Ie3962832f1e1a646592f78ceccafa3a60d17572b
Merge topic 'unique-atoms-bonds' into master

ff1db730 Extended the unique id foundations in Molecule
4b346206 Added equality and inequality operators for atoms and bonds