Support modified residues in Sequence

src/mol-app/ui/visualization/sequence-view.tsx

src/mol-model/sequence/constants.ts

src/mol-model/sequence/sequence.ts

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

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

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