basic transparency

src/apps/render-test/state.ts

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

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

src/mol-geo/representation/volume/surface.ts

src/mol-gl/_spec/renderer.spec.ts

src/mol-gl/renderable/mesh.ts

src/mol-gl/renderable/point.ts

src/mol-gl/renderable/util.ts

src/mol-gl/renderer.ts

src/mol-gl/scene.ts

src/mol-gl/shader/mesh.frag

src/mol-gl/shader/point.frag

src/mol-view/viewer.ts