code: def app_start(device_id, app_id):
      
      if not is_valid_app_id(app_id):
          abort(403)
      if not is_valid_device_id(device_id):
          abort(403)
      if device_id not in devices:
          abort(404)
  
      success = devices[device_id].launch_app(app_id)
      return jsonify(success=success)
docs: Starts an app with corresponding package name