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/reducers/connections.js

@@ -354,6 +354,7 @@ export const selectPlugin = (payload: {|
   type: 'SELECT_PLUGIN',
   payload,
 });
+
 export const userPreferredPlugin = (payload: string): Action => ({
   type: 'SELECT_USER_PREFERRED_PLUGIN',
   payload,