plumbing to make auth0-less users work in the website (#2398)

* [www] plumbing to make auth0-less users work in the website

* [www] fix and separate verification-email feature

* [snack] nickname->username

* [www] fix plubming, expo admin

* [xde] fix toolbar nickname -> username

* [snack] nickname -> username

* [www] deprecate nickname, support it going backwards

* [www] nickname -> username

* [www] fix flow errors

fbshipit-source-id: 7473327

src/ui/toolbar/ToolBar.js

@@ -71,7 +71,7 @@ const mapStateToProps = (state, props) => {
 
 class ToolBar extends React.Component {
   static data = ({ auth }: AppState) => ({
-    userName: auth.user && auth.user.nickname,
+    userName: auth.user && auth.user.username,
   });
 
   props: Props;