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/ui/components/ButtonNavigationGroup.tsx

@@ -0,0 +1,38 @@
+/**
+ * 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 ButtonGroup from './ButtonGroup';
+import Button from './Button';
+import React from 'react';
+
+/**
+ * Button group to navigate back and forth.
+ */
+export default function ButtonNavigationGroup(props: {
+  /** Back button is enabled */
+  canGoBack: boolean;
+  /** Forwards button is enabled */
+  canGoForward: boolean;
+  /** Callback when back button is clicked */
+  onBack: () => void;
+  /** Callback when forwards button is clicked */
+  onForward: () => void;
+}) {
+  return (
+    <ButtonGroup>
+      <Button disabled={!props.canGoBack} onClick={props.onBack}>
+        {'<'}
+      </Button>
+
+      <Button disabled={!props.canGoForward} onClick={props.onForward}>
+        {'<'}
+      </Button>
+    </ButtonGroup>
+  );
+}