improved normals and transparency

src/apps/render-test/state.ts

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

src/mol-geo/util.ts

src/mol-gl/renderable/mesh.ts

src/mol-gl/shader-code.ts

src/mol-gl/shader/mesh.frag

src/mol-gl/shader/mesh.vert

src/mol-math/linear-algebra/3d/mat3.ts

src/mol-math/linear-algebra/3d/vec3.ts

src/mol-view/viewer.ts