Move ProtocolUtilities to new package
CraftBukkit allows zero firework power
https://github.com/Bukkit/CraftBukkit/blob/master/src/main/java/org/bukkit/craftbukkit/inventory/CraftMetaFirework.java#L382
According to that, zero power is not disallowed by the API
But, will it work as intended? Time for testing.
Constants class improvements
Added new fields
Added method to get number of ticks from number of seconds
Added Constants#MAXIMUM_FOOD_LEVEL, representing a player's max food
level