avoid cloning of structure repr params

src/mol-repr/structure/representation/ball-and-stick.ts

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

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

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

src/mol-repr/structure/representation/gaussian-volume.ts

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

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

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

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

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

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