Zip file download of annexed data without creating zip file

A zip function that reads annexed data already exists in [libgin/archive](https://github.com/G-Node/libgin/tree/master/libgin/archive). It might be possible to write the output of the zip function to the web response writer, feeding the data to the response without creating it on disk and without waiting for the zip to finish.

The downsides will be that the download can't be resumed on interruption and there's no way of knowing the final size beforehand, so no progress.