Support OpenFF's LibraryCharges

[martimunicoy]

Description

Currently, we obtain partial charges with antechamber. As far as I know, in the future the OpenFF Toolkit will has its own library for partial charges. They have already built some examples like the tip3p.offxml forcefield for water where there is an example of the LibraryCharges usage.

Solution

When parameterizing with OpenFF the default option to get partial charges should be their own LibraryCharges (at least, once they fully support the feature).