[IMP-dev] Death to objects

A possible fatal blow for objects came up when talking with Jeremy.

Lets say we load a PDB file. It creates a bunch of Particles, some of which are AtomParticles, some ResidueParticles etc. Now it happens I am doing coarse grained modeling, so I only care about the Residues and want to approximate them by a sphere. I have no way of adding a radius attribute to the already existing particle. I have to copy the particle to a new ResidueWithRadiusParticle (and delete the old one) or add a new particle linked to the existing one. Deleting the old residue would break all existing restraints which use the particle.