add an option to ignore hydrogen atoms

[UnixJunkie]

at least during parsing of MOL2 files there is some work saved already in the branch https://github.com/UnixJunkie/ACPC/tree/no_hydrogens

[UnixJunkie]

Maybe the proper way is to add hydrogen contributions to the heavy atoms they are attached to; as is done in the hydrophobic space. Also, we must check if ignoring hydrogens decrease the performance.