Reset to default feature for properties/settings

[rwb27]

It would be nice to be able to "reset" individual settings or properties to their default value. For DataSetting or DataProperty this is easy: there's a ready-made default value we can use. For their functional counterparts it's not obvious to me how to do it, because there's never a default defined.

This issue is intended to capture some discussion on that topic. Once PropertyInfo et al is merged, it should be quite straightforward to get a reset feature implemented.