mol-plugin-ui: general refactoring & code improvements

src/mol-plugin-ui/controls/action-menu.tsx

src/mol-plugin-ui/controls/color.tsx

src/mol-plugin-ui/controls/common.tsx

src/mol-plugin-ui/controls/parameters.tsx

src/mol-plugin-ui/skin/base/components/controls.scss

src/mol-plugin-ui/skin/base/components/temp.scss

src/mol-plugin-ui/skin/base/components/transformer.scss

src/mol-plugin-ui/state/common.tsx

src/mol-plugin-ui/structure/components.tsx

src/mol-plugin-ui/structure/focus.tsx

src/mol-plugin-ui/structure/measurements.tsx

src/mol-plugin-ui/structure/selection.tsx

src/mol-plugin-ui/viewport/help.tsx

...havior/dynamic/custom-props/rcsb/ui/assembly-symmetry.tsx