Comment 2 for bug 636193

In working on this issue I've found that feature flag names and scopes
aren't registered before use, therefore all possible feature flags and
scopes can not be listed given the system as it stands.

To complete this feature request we will need a registry of feature flag
names that specifies the allowable names and modify the code to raise an
exception when an unregistered feature flag is requested.

Scopes are generated by code (ScopesFromRequest.lookup()) so a similar
(but slightly more dynamic) registry would be required for them.

Is the above approach acceptable? Was there another approach in mind
when this bug was filed that I'm missing?