add an ability to feature previews to pass a function that, given the request, determines whether to display that feature preview on the Feature Previews page.
add an ability to feature previews to pass a function that, given the request, determines whether to display that feature preview on the Feature Previews page.

dimagi/commcare-hq,dimagi/commcare-hq,dimagi/commcare-hq,dimagi/commcare-hq,dimagi/commcare-hq