* - added two convenience functions to allow miniming all molecule confs with a pre-generated force-field (e.g., to use constraints)
- removed a lot of code duplication between Code/GraphMol/ForceFieldHelpers/MMFF/MMFF.h Code/GraphMol/ForceFieldHelpers/UFF/UFF.h
- homogenized the nonBondedThreshold to 100.0 across all MMFF functions
* - avoided code duplication
- added tests
- added PRECONDITION clauses