various ui tweaks, added CollapsableControls

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

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

src/mol-plugin/skin/base/icons.scss

src/mol-plugin/ui/base.tsx

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

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

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

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

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