mol-model: added parent & coordinate system to Structure

src/mol-model/structure/query/queries/filters.ts

src/mol-model/structure/query/queries/generators.ts

src/mol-model/structure/query/queries/internal.ts

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

src/mol-model/structure/query/utils/structure-set.ts

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

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

src/mol-model/structure/structure/util/subset-builder.ts

...l-model/structure/structure/util/unique-subset-builder.ts