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/pathUtils.tsx

@@ -0,0 +1,31 @@
+/**
+ * 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 path from 'path';
+import fs from 'fs';
+import {remote} from 'electron';
+
+let _staticPath = '';
+
+export function getStaticPath() {
+  if (_staticPath) {
+    return _staticPath;
+  }
+  _staticPath = path.resolve(__dirname, '..', '..', '..', 'static');
+  if (fs.existsSync(_staticPath)) {
+    return _staticPath;
+  }
+  if (remote && fs.existsSync(remote.app.getAppPath())) {
+    _staticPath = path.join(remote.app.getAppPath());
+  }
+  if (!fs.existsSync(_staticPath)) {
+    throw new Error('Static path does not exist: ' + _staticPath);
+  }
+  return _staticPath;
+}