cleanup, cylinder links & mesh builder

src/mol-geo/primitive/cylinder.ts

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

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

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

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

src/mol-geo/representation/structure/visual/util/link.ts

src/mol-geo/shape/mesh-builder.ts