The ESS singleton. Gives easy access to entity and spell related data, providing easy lookups. Make sure that you add everything both server and clientside before use, because the system uses ids (get_id()) for server clinet communications. This also means that ids should be unique per resources for every ESS-related resources. For example you shouldn't register 2 spells with id 1 (you will get an error), but you can register a [Spell] with id1 and an [Aura] with an id 1. Also grants access easy to ESS-related project settings.