Error message handling

[childss]

Error message bubbling/handling needs more research and enhancement. When I first implemented templates/error.hbs and templates/secured/error.hbs I only created the secured one because errors were inconsistently bubbling up to the global error handler. Now it seems (f48f095) even authorization failures aren't being handled properly by the secured one in certain circumstances.

This says to me that I don't actually understand how errors fly around the app.

[lvgelder]

I don't understand errors in Ember either. For now I've just fixed the case where someone accesses the /users page without permission. Neither {{message}} nor {{error}} return anything useful.

I've left {{message}} on there in case it ever gets set correctly but I'm doubtful.