improved accessible-surface-area computation

src/mol-model-props/computed/accessible-surface-area.ts

...l-props/computed/accessible-surface-area/shrake-rupley.ts

...ps/computed/accessible-surface-area/shrake-rupley/area.ts

.../computed/accessible-surface-area/shrake-rupley/common.ts

...mputed/accessible-surface-area/shrake-rupley/normalize.ts

...s/computed/accessible-surface-area/shrake-rupley/radii.ts

src/mol-theme/color.ts

src/mol-theme/color/accessible-surface-area.ts

src/tests/browser/render-asa.ts

src/tests/browser/render-structure.ts

webpack.config.js