Per-user-group security settings and allow/block lists

Support multiple user groups with different security settings and different block/allow lists. Forward-facing users (sales, buying, and similar roles) do not want banners on domains they regularly talk to, while regular users should still see the graymail banners on those senders. Users who tend to click on everything could be placed in a group with stricter settings. When marking an email after a report, allow choosing whether the allow/block entry applies just to the group the user is a part of, or to the company as a whole.