assembly parsing from mmCIF

src/mol-math/geometry/symmetry-operator.ts

src/mol-math/linear-algebra/3d.ts

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

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

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

src/perf-tests/structure.ts