Add a headheal command. Change golden head config to be total hearts

Added command /headheal <amount> with permission UHC.goldenhead.command default op. Sets the total amounts of hearts a golden head will heal. Changed amountExtra config option to amountTotal and now sets the total amount of half hearts healed instead of extra amount. Setting to 4 or lower will make it 4 due to the original golden apple regen overwriting ours.