mol-plugin: improving UI (mostly animation controls in viewport)

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

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

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

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

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

src/mol-plugin/ui/controls.tsx

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

src/mol-plugin/ui/plugin.tsx

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

src/mol-plugin/ui/viewport.tsx