Import from exported file

Summary:
This diff adds the feature to import the exported flipper data. It has the following features

- Dialog to select the file
- Merges the data with an existing store.

Reviewed By: danielbuechele

Differential Revision: D13901944

fbshipit-source-id: 1b9755735419732a34254bdc39d911bcb51ad8fe

src/devices/AndroidDevice.js

@@ -78,7 +78,7 @@ export default class AndroidDevice extends BaseDevice {
     });
   }
 
-  spawnShell(): DeviceShell {
+  spawnShell(): ?DeviceShell {
     return child_process.spawn('adb', ['-s', this.serial, 'shell', '-t', '-t']);
   }
 }