Add API to control scaled health. Adds BUKKIT-4590

This commit implements the ability to set the scale of hearts that the client renders.  When the Packet44UpdateAttributes packet is sent, the max health attribute is replaced with a scaled version, to preserve the scaled health illusion clientside.

In order to accurately display the scaled health for players, a true health is stored within CraftPlayer, and the datawatcher now stores the scaled health. The getHealth() method for players still returns their true health.

Changed setHealth() within EntityLiving to appropriately handle health for instances of EntityPlayer. Inlined a call to setHealth(getMaxHealth()) within the EntityLiving constructor to work around CraftEntity instantiation.

Additionally fixes the health values sent when eating food within FoodMetaData and ItemFood, which previously sent the unscaled health; this commit alters them to send the properly scaled health.

Additionally fixes BUKKIT-4535, BUKKIT-4536, and BUKKIT-4127