Earlier operator metadata is cached in the browser

[shengquan-ni]

After the ScatterPlot operator gets updated and the server restarts, the ScatterPlot operator doesn't show a newly added "Color-Column" option. After the user logs out and re-logs in, the problem is solved. I think it's due to client-site caching. If so, it will be good to have a way to force the client to clear their local cache.