Gp builder: how does it deal with existing glycans?

Remove the existing glycans from the glycosites and rebuild them, or
Complete glycan structures on top of the existing ones?

Oliver: If the user does not request MDprep (default behaviour now, will be an option in v.1.1) then anything in the PDB file stays. This will mess up sites where there is a glycan and we try to add a glycan on top.
If the user requests MDprep, we need to delete existing glycans.

In future, we want to be able to identify existing glycans, rename those residues to GLYCAM format, build on top of them and allow options for whether they are frozen or not. Requires a lot of work at the gmml2 level.