convert to emotion

Summary:
My benchmarks have shown react-emotion to be faster than the current implementation of `styled`. For this reason, I am converting all styling to [emotion](https://emotion.sh).

Benchmark results:
{F136839093}

The syntax is very similar between the two libraries. The main difference is that emotion only allows a single function for the whole style attribute, whereas the old implementation had functions for every style-attirbute.

Before:
```
{
  color: props => props.color,
  fontSize: props => props.size,
}
```

After:
```
props => ({
  color: props.color,
  fontSize: props.size,
})
```

Reviewed By: jknoxville

Differential Revision: D9479893

fbshipit-source-id: 2c39e4618f7e52ceacb67bbec8ae26114025723f

src/ui/index.js

@@ -4,9 +4,7 @@
  * LICENSE file in the root directory of this source tree.
  * @format
  */
-export type {StyledComponent} from './styled/index.js';
 
-//
 export {default as Button} from './components/Button.js';
 export {default as ToggleButton} from './components/ToggleSwitch.js';
 export {
@@ -26,10 +24,6 @@ export {default as LoadingIndicator} from './components/LoadingIndicator.js';
 //
 export {default as Popover} from './components/Popover.js';
 
-//
-export {default as ClickableList} from './components/ClickableList.js';
-export {default as ClickableListItem} from './components/ClickableListItem.js';
-
 //
 export type {
   TableColumns,