Add option to restrict number of simultaneous downloads

Hopefully this would be a simple little addition for the Plex player. Currently when multiple items are selected for download they all attempt to download simultaneously. This new setting would allow the user to limit the number of simultaneous downloads - from 1 to unlimited.

I know downloads isn’t a high priority feature for Plex, but it is really very useful for bandwidth limited, low spec servers.

While the activity drop-down shows all the downloads it will grab, it only downloads 2 at a time.