Removed leftover print_r from FilterStack
Further model protection

No long able to find a model using a "protected" variable (e.g. password
for a user).
ActiveRecord updated

- Deleted `Collection` class from `Common`
- Model & ModelCollection now implement `JsonSerializable`
- Model now uses ModelCursor to open up MongoCursor API
- WebController updated to use the `fetch` method with models.