Fetch latest image feature available on Illinois LSST Server

The basic feature of fetching latest image is now available on Illinois LSST server. It will automatically try to fetch and display a new image file from another visualization/image server (which currently also runs on the same server machine). It might need few seconds to update. User can also pause or resume by the button.

The visualization-server from @tony_johnson right now always returns an empty FITS file. So Firefly is probably displaying a default one and we won’t see any change in the latest image. We will need to test the performance once the server can return URIs of real images.