wip, link repr coloring

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

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

...mol-geo/representation/structure/visual/element-sphere.ts

...presentation/structure/visual/intra-unit-link-cylinder.ts

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

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

src/mol-geo/theme/structure/color/element-symbol.ts

src/mol-geo/theme/structure/color/index.ts

src/mol-geo/util/color-data.ts