Add a quota to the email address restriction list in management.java

The select box item for download at https://staging.profitsharingprojects.com/carlist and described in this discussion thread https://www.screencast.com/t/i31QsR0dXOP is currently restricted to be available for only people with a specific email address. I need to further restrict it so that each user is authorized only for their specified number of downloads and I would start with only one authorized for most people.

How can I add this quota functionality?

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