Admin-defined default drilldowns

Our users get very confused with the different options for drilldowns in reports. Without a deep understanding of how the data is recorded, ordinary users can't reliably make the right choices.

I'd like each prop and eVar to be able to have admin-defined default drilldowns, so that we can go through them and decide which ones make sense.

Obviously for power users, there needs to still be the "Advanced" option of drilldowns.