cleaned-up gaussian surface code

src/apps/canvas/component/structure-representation.tsx

src/apps/canvas/structure-view.ts

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

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

...representation/structure/visual/gaussian-density-point.ts

.../representation/structure/visual/gaussian-surface-mesh.ts

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