added EmptyLoci

src/mol-geo/representation/index.ts

src/mol-geo/representation/structure/bond.ts

src/mol-geo/representation/structure/index.ts

src/mol-geo/representation/structure/point.ts

src/mol-geo/representation/structure/spacefill.ts

src/mol-geo/representation/volume/index.ts

src/mol-geo/representation/volume/surface.ts

src/mol-model/loci.ts

src/mol-view/label.ts