Cache users by objectID, and clear cache when updated via master key (fixes #1836) (#1844)

* Cache users by objectID, and clear cache when updated via master key

* Go back to caching by session token. Clear out cache by querying _Session when user is modified with Master Key (ew, hopefully that can be improved later)

* Fix issue with user updates from different sessions causing stale reads

* Tests aren't transpiled...

* Still not transpiled

src/Auth.js

@@ -72,7 +72,6 @@ var getAuthForSessionToken = function({ config, sessionToken, installationId } =
       obj['className'] = '_User';
       obj['sessionToken'] = sessionToken;
       config.cacheController.user.put(sessionToken, obj);
-
       let userObject = Parse.Object.fromJSON(obj);
       return new Auth({config, isMaster: false, installationId, user: userObject});
     });