Refactor LookupNames#add_subtaxa for performance
Refactor LookupNames#add_subtaxa for performance

- Use a single AR method chain instead of multiple queries
- AR `distinct` instead of Rails `uniq`
- eliminate intermediate assignments

MushroomObserver/mushroom-observer,MushroomObserver/mushroom-observer,MushroomObserver/mushroom-observer,MushroomObserver/mushroom-observer,MushroomObserver/mushroom-observer,MushroomObserver/mushroom-observer,MushroomObserver/mushroom-observer