wip, refactoring of representations and visuals

src/mol-app/ui/transform/file-loader.tsx

src/mol-app/ui/transform/url-loader.tsx

src/mol-geo/representation/index.ts

...ol-geo/representation/structure/complex-representation.ts

src/mol-geo/representation/structure/complex-visual.ts

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

...l-geo/representation/structure/representation/backbone.ts

...representation/structure/representation/ball-and-stick.ts

...o/representation/structure/representation/carbohydrate.ts

...ol-geo/representation/structure/representation/cartoon.ts

...esentation/structure/representation/distance-restraint.ts

...-geo/representation/structure/representation/spacefill.ts

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

src/mol-geo/representation/structure/units-visual.ts

...esentation/structure/visual/carbohydrate-link-cylinder.ts

...presentation/structure/visual/carbohydrate-symbol-mesh.ts

...ntation/structure/visual/cross-link-restraint-cylinder.ts

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

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

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