updating UI documentation

Summary:
adding documentation for more of our UI components.

Deleted some unused components, which were not working anyways.

Reviewed By: jknoxville

Differential Revision: D12896109

fbshipit-source-id: 959c7864240883869ad67283f80a3c189b94bf00

src/ui/components/ButtonGroup.js

@@ -21,12 +21,13 @@ const ButtonGroupContainer = styled('div')({
 /**
  * Group a series of buttons together.
  *
- * @example List of buttons
+ * ```jsx
  *   <ButtonGroup>
  *     <Button>One</Button>
  *     <Button>Two</Button>
  *     <Button>Three</Button>
  *   </ButtonGroup>
+ * ```
  */
 export default class ButtonGroup extends Component<{
   children: React$Node,