wip, sync/async visual create/update

src/mol-repr/representation.ts

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

src/mol-repr/structure/complex-visual.ts

src/mol-repr/structure/registry.ts

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

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

src/mol-repr/structure/units-visual.ts

src/mol-repr/structure/visual/gaussian-density-point.ts

src/mol-repr/structure/visual/gaussian-density-volume.ts

src/mol-repr/structure/visual/gaussian-surface-mesh.ts

src/mol-repr/structure/visual/gaussian-surface-wireframe.ts