added polymer-id color scheme, removed model.asymIdSerialMap

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

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

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

src/mol-repr/structure/representation/molecular-surface.ts

src/mol-theme/color.ts

src/mol-theme/color/chain-id.ts

src/mol-theme/color/polymer-id.ts