Terminal conjugated bonds in distance geometry checks

[chmnk]

A follow-up of #62, inspired by what we have in https://github.com/rdkit/rdkit/blob/master/Code/GraphMol/MolAlign/AlignMolecules.cpp#L27

Changes the distance geometry check for some terminal conjugated bonds:

• gets the bonds from a SMARTS match to a conjugated bond template
• since to my understanding, the conjugated bonds are usually between a single/double, it groups all those bonds by atom types
• for each set of atom types (C--O, N--O), the lower/higher bound will be the minimum/maximum of the lower/higher bounds with this atom type.