Load routes to device during init (#1491)

Summary:
This is a replacement for PR https://github.com/facebook/flipper/pull/1486 which had the wrong username

When the network plugin is loaded, the route table in the device is empty.  It needs to be populated with whatever routes have already been created and saved in local storage.  Otherwise, the user would need to modify the routes to force an update.

Issue is described here - https://github.com/facebook/flipper/issues/1476

## Changelog

Routes updated in device when plugin is initialized

Pull Request resolved: https://github.com/facebook/flipper/pull/1491

Test Plan:
1. Create a mock for the get request in the sample Android app
2. Kill the app
3. Start the app
4. Issue the get request in the app
5. Verify that the request is mocked in the Network plugin

![image](https://user-images.githubusercontent.com/69264583/90853263-37648200-e33f-11ea-8ab1-afc09395e62e.png)

Reviewed By: passy

Differential Revision: D23292355

Pulled By: mweststrate

fbshipit-source-id: 2fe16e9067a627cae02a4b1db422952d364fd036

desktop/plugins/network/index.tsx

@@ -342,6 +342,7 @@ export default class extends FlipperPlugin<State, any, PersistedState> {
         showMockResponseDialog: false,
         nextRouteId: Object.keys(routes).length,
       });
+      informClientMockChange(routes);
     });
 
     this.setState(this.parseDeepLinkPayload(this.props.deepLinkPayload));