prettier 2

Summary:
Quick notes:

- This looks worse than it is. It adds mandatory parentheses to single argument lambdas. Lots of outrage on Twitter about it, personally I'm {emoji:1f937_200d_2642} about it.
- Space before function, e.g. `a = function ()` is now enforced. I like this because both were fine before.
- I added `eslint-config-prettier` to the config because otherwise a ton of rules conflict with eslint itself.

Close https://github.com/facebook/flipper/pull/915

Reviewed By: jknoxville

Differential Revision: D20594929

fbshipit-source-id: ca1c65376b90e009550dd6d1f4e0831d32cbff03

desktop/plugins/layout/ToolbarIcon.tsx

@@ -24,7 +24,7 @@ const ToolbarIcon = styled.div({
   position: 'relative', // for settings popover positioning
 });
 
-export default function(props: Props) {
+export default function (props: Props) {
   return (
     <ToolbarIcon onClick={props.onClick} title={props.title}>
       <Glyph