currently the container doesn't depend on ember, this is likely fine for today, but likely something we will need to think about for future flags

an idea would be:
```javascript
// continue using this externally.
Ember.MODEL_FACTORY_INJECTIONS
```

```javascript
// within ember, once Container is loaded we pro
Ember.Container.MODEL_FACTORY_INJECTIONS == !!Ember.MODEL_FACTORY_INJECTIONS 
```

downside is that toggling Ember.MODEL_FACTORY_INJECTIONS, to late wont have any effect.

Another option is just to put the flag on the Container...