Add support for commonly used co-factors

[VGPReys]

Desired feature/enhancement

It would be nice to add support for some of the commonly used co-factors, such as ATP, ADP, GTP, etc..

Motivation

Those co-factors can be modeled using AF3 webserver, and therefore I am expecting scientists to come to haddock3 to refine their complexes.
But for now, as we do not have an easy parameter/topology generation tool embedded in haddock3, it is tricky to obtain those.