tweaks to represent ihm models

src/apps/render-test/state.ts

src/apps/render-test/utils/index.ts

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

src/mol-geo/representation/structure/utils.ts

src/mol-geo/theme/structure/color/chain-id.ts

src/mol-geo/theme/structure/color/element-index.ts

src/mol-geo/theme/structure/color/index.ts

src/mol-view/viewer.ts