Added IntGraph and using it for IntraUnitBonds

src/apps/structure-info/model.ts

src/mol-math/graph.ts

src/mol-math/graph/_spec/int-graph.spec.ts

src/mol-math/graph/int/graph.ts

src/mol-model/sequence/TODO

src/mol-model/sequence/constants.ts

src/mol-model/sequence/sequence.ts

...mol-model/structure/structure/unit/bonds/intra-compute.ts

src/mol-model/structure/structure/unit/bonds/intra-data.ts