added custom color theme, color refactoring

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

src/mol-view/theme/color.ts

src/mol-view/theme/color/carbohydrate-symbol.ts

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

src/mol-view/theme/color/cross-link.ts

src/mol-view/theme/color/custom.ts

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

src/mol-view/theme/color/element-symbol.ts

src/mol-view/theme/color/shape-group.ts

src/mol-view/theme/color/uniform.ts

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