Yarn workspaces

Summary:
1) moved "sonar/desktop/src" to "sonar/desktop/app/src", so "app" is now a separate package containing the core Flipper app code
2) Configured yarn workspaces with the root in "sonar/desktop": app, static, pkg, doctor, headless-tests. Plugins are not included for now, I plan to do this later.

Reviewed By: jknoxville

Differential Revision: D20535782

fbshipit-source-id: 600b2301960f37c7d72166e0d04eba462bec9fc1

desktop/app/src/utils/persistor.tsx

@@ -0,0 +1,22 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @format
+ */
+
+import {Persistor} from 'redux-persist';
+
+let _persistor: Persistor | null = null;
+
+export function setPersistor(persistor: Persistor) {
+  _persistor = persistor;
+}
+
+export function flush(): Promise<void> {
+  return _persistor
+    ? _persistor.flush()
+    : Promise.reject(new Error('Persistor not set.'));
+}