color refactoring

src/mol-model-props/rcsb/themes/assembly-symmetry-cluster.ts

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

src/mol-theme/color/element-index.ts

src/mol-theme/color/entity-source.ts

src/mol-theme/color/model-index.ts

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

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

src/mol-theme/color/unit-index.ts

src/mol-util/color/palette.ts