If enable_extension fails in the first DB migration, it should provide a better error about what to do.

[tpendragon]

Right now new users of Valkyrie who run db migrations as users that don't have permissions to add extensions get an error they don't really know how to handle.

We should catch that error somehow and say something like

"You don't have permission to add the UUID-OSSP extension. Your database administrator may need to enable this, otherwise use a superuser to add this extension to postgres"