Add first version of Molecule proxy
Expand Molecule proxy

 * Add 'create', 'delete', 'load' and 'name'.
 * Fix 'molecule' property.
 * Rewrite tests.
Add molecule manager and MOLECULES instance.

 * Add manager over all molecules.
 * Create its MOLECULES instance.
Add Atom proxy object

 * Add Atom object as a representation of one atom in molecule.