improved bond handling

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

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

src/mol-plugin/util/structure-selection-helper.ts

src/mol-repr/structure/visual/bond-inter-unit-cylinder.ts

src/mol-repr/structure/visual/bond-intra-unit-cylinder.ts

src/mol-repr/structure/visual/util/bond.ts

src/mol-script/runtime/query/table.ts