[B + C] FoodLevelChangeEvent improvements - Adds BUKKIT-3581

a) This PR will allow developers to get the saturation level from FoodLevelChangeEvents, instead of only the food level. Currently, while it's possible to get / set the saturation level for a player, it's not possible to know how a given food changes the saturation.

b) Just like being able to work with the food level, being able to work with the saturation level is important for plugins that modify this event, as the raw food level / hunger is only one part of the food mechanic, and without having the saturation value it's impossible to completely alter the vanilla behavior.

c) This would not break existing plugins working from the Bukkit API, as the old FoodLevelChange event would still exist, but would return 0 for the saturation level. The raw CB event, however, would change, but it has long been said that relying on CB code to remain constant is unreliable, and breaks rather consistently.

CraftBukkit PR: https://github.com/Bukkit/CraftBukkit/pull/1078
`Gets`