Serialize Store

Summary:
This diff adds the capability to export the flipper data to a file. With this diff you can click on the "Export Flipper" option from the "Edit" menu in menubar. It will export it in the file at this location

`~/.flipper/MessageLogs.json`

We do not exactly export the store, but just the important part of it. We export in the following format

```
{
fileVersion: '1.0',
device: {
   os: 'iOS',
   title: 'iPhone 7',
   serial: '',
   deviceType: 'physical',
  },
clients: [
   {
    query: {
       app: 'Facebook',
      },
      d: '12345678'
     },
   {
    query: {
       app: 'Instagram',
      },
    id: '12345678'
   }
],
store: {
   pluginState: {},
   notifications: {}
  }
}

```

In next diff I will add the capability to select the folder to export the file too.

Reviewed By: danielbuechele

Differential Revision: D13751963

fbshipit-source-id: 7d3d49c6adf8145b2181d2332c7dbd589155cec3

src/MenuBar.js

@@ -6,7 +6,8 @@
  */
 
 import type {FlipperPlugin, FlipperDevicePlugin} from './plugin.js';
-
+import {exportStoreToFile} from './utils/exportData.js';
+import type {Store} from './reducers/';
 import electron from 'electron';
 
 export type DefaultKeyboardAction = 'clear' | 'goToBottom' | 'createPaste';
@@ -64,9 +65,13 @@ function actionHandler(action: string) {
 
 export function setupMenuBar(
   plugins: Array<Class<FlipperPlugin<> | FlipperDevicePlugin<>>>,
+  store: Store,
 ) {
-  const template = getTemplate(electron.remote.app, electron.remote.shell);
-
+  const template = getTemplate(
+    electron.remote.app,
+    electron.remote.shell,
+    store,
+  );
   // collect all keyboard actions from all plugins
   const registeredActions: Set<?KeyboardAction> = new Set(
     plugins
@@ -169,8 +174,24 @@ export function activateMenuItems(
   );
 }
 
-function getTemplate(app: Object, shell: Object): Array<MenuItem> {
+function getTemplate(
+  app: Object,
+  shell: Object,
+  store: Store,
+): Array<MenuItem> {
   const template = [
+    {
+      label: 'File',
+      submenu: [
+        {
+          label: 'Export Data',
+          role: 'export',
+          click: function(item: Object, focusedWindow: Object) {
+            exportStoreToFile(store);
+          },
+        },
+      ],
+    },
     {
       label: 'Edit',
       submenu: [