patch and background transparency

src/mol-canvas3d/passes/draw.ts

src/mol-geo/geometry/transparency-data.ts

src/mol-gl/renderable.ts

src/mol-gl/renderable/direct-volume.ts

src/mol-gl/renderable/schema.ts

src/mol-gl/renderer.ts

src/mol-gl/shader-code.ts

src/mol-gl/shader/evaluate-wboit.frag.ts

src/mol-gl/webgl/context.ts

src/mol-gl/webgl/program.ts

src/mol-repr/visual.ts