Calculate & depict dipole moment vector

[ghutchis]

Version 1.0 / 1.2 had a dipole moment vector render option. For teaching purposes it would be great to bring it back:

• Calculate dipole moment (different models)
• Input custom vector
• Render it as an arrow
• Store the calculated dipole moment as a property for the molecular properties dialog
• Read / Write dipole moments to CJSON
• Add support for read / write in other formats, e.g. Open Babel