Add OpenMM module

[joaomcteixeira]

The code presented in this commit was entirely done by Ivar de Leeuw during his Master course: Major Research Project (GSLS), academic year 2021-2022.

I am pushing the code after Ivar's request and in its exact original form.

In the next commits, the team will work on Ivar's code to accommodate it fully to the HADDOCK3 project.

Thanks, Ivar, for all your great work and best luck with your future studies!