improve handling of coarse grained models

src/mol-model-props/computed/interactions.ts

src/mol-model-props/computed/representations/interactions.ts

src/mol-model/structure/model/model.ts

src/mol-model/structure/structure/structure.ts

...mol-model/structure/structure/unit/bonds/inter-compute.ts

...mol-model/structure/structure/unit/bonds/intra-compute.ts

...l-plugin-state/builder/structure/representation-preset.ts

...avior/dynamic/selection/structure-focus-representation.ts

src/mol-repr/structure/representation/spacefill.ts

src/mol-repr/structure/visual/element-point.ts