added support for cyclic atomic polymers

.../representation/structure/visual/nucleotide-block-mesh.ts

src/mol-geo/representation/structure/visual/util/polymer.ts

src/mol-model/structure/model/formats/mmcif/atomic.ts

src/mol-model/structure/model/properties/atomic/hierarchy.ts

...l-model/structure/model/properties/utils/atomic-ranges.ts

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

src/mol-model/structure/util.ts

src/mol-view/stage.ts