WIP. Adding A/B/C Testing

I think it would be more readable to use an options hash... so we don't have to go look up what nil/true/etc means. so the call would be like:
````
get_hint_from_source_internal including: LevelSourceHint::CROWDSOURCED
get_hint_from_source_internal excluding: LevelSourceHint::CROWDSOURCED
get_hint_from_source_internal # hints from all sources
````