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

flow-typed/npm/react-emotion_vx.x.x.js

@@ -0,0 +1,60 @@
+// flow-typed signature: 69f0585b3bbc433c0c0eb3d242636c6d
+// flow-typed version: <<STUB>>/react-emotion_v9.2.6/flow_v0.76.0
+
+/**
+ * This is an autogenerated libdef stub for:
+ *
+ *   'react-emotion'
+ *
+ * Fill this stub out by replacing all the `any` types.
+ *
+ * Once filled out, we encourage you to share your work with the
+ * community by sending a pull request to:
+ * https://github.com/flowtype/flow-typed
+ */
+
+declare module 'react-emotion' {
+  declare module.exports: any;
+}
+
+/**
+ * We include stubs for each file inside this npm package in case you need to
+ * require those files directly. Feel free to delete any files that aren't
+ * needed.
+ */
+declare module 'react-emotion/dist/emotion.umd.min' {
+  declare module.exports: any;
+}
+
+declare module 'react-emotion/dist/index.cjs' {
+  declare module.exports: any;
+}
+
+declare module 'react-emotion/dist/index.esm' {
+  declare module.exports: any;
+}
+
+declare module 'react-emotion/macro' {
+  declare module.exports: any;
+}
+
+declare module 'react-emotion/src/index' {
+  declare module.exports: any;
+}
+
+// Filename aliases
+declare module 'react-emotion/dist/emotion.umd.min.js' {
+  declare module.exports: $Exports<'react-emotion/dist/emotion.umd.min'>;
+}
+declare module 'react-emotion/dist/index.cjs.js' {
+  declare module.exports: $Exports<'react-emotion/dist/index.cjs'>;
+}
+declare module 'react-emotion/dist/index.esm.js' {
+  declare module.exports: $Exports<'react-emotion/dist/index.esm'>;
+}
+declare module 'react-emotion/macro.js' {
+  declare module.exports: $Exports<'react-emotion/macro'>;
+}
+declare module 'react-emotion/src/index.js' {
+  declare module.exports: $Exports<'react-emotion/src/index'>;
+}