Allow user to set size of ghost atom

Is your feature request related to a problem? Please describe. Sometimes a user might want to show a generic attachment point - coloured spheres in place of R1, R2 etc are all the rage in chemistry talks it seems.

Sometimes a user might want to depict a molecule bound to a nanoparticle or something else "blobby".

Describe the solution you'd like If the size of a ghost atom was customizable, that would provide a convenient way to create such depictions.

Describe alternatives you've considered Another option would be an additional atom type that is specifically designed to function as a "blob", but that seems unnecessary.