loci helper methods, isEmpty

src/mol-model/loci.ts

src/mol-model/shape/shape.ts

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

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

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

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

src/mol-plugin/ui/sequence/sequence.tsx

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

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

src/mol-repr/structure/complex-representation.ts

src/mol-repr/structure/units-representation.ts