add features necessary for general use of adult bodies on child pawns

• add settings ui for toggling whether kids can wear adult or child apparel
• add a patch for LifeStageWorker_HumanlikeAdult to ensure a child moves to adulthood correctly when not using a child body
• expose the functionality needed to implement Body Changer as a public api, a collection of extensions to rimworld's types
• provide a hook for coordinating with mods that link against this one