mol-plugin: Structure components UI

src/mol-plugin-state/actions/structure.ts

src/mol-plugin-ui/controls.tsx

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

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

src/mol-plugin-ui/left-panel.tsx

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

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

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

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

src/mol-plugin/behavior/static/camera.ts

src/mol-plugin/commands.ts