Refactor & expand utilities. Add fake enchantment for ItemBuilder

[njsharpe]

• Split Utility into StringUtil & NumberUtil for organization.
• Added functions to StringUtil that may come in handy.
• Added min(...) to NumberUtil for consistency.
• Added fake enchantment for use in ItemBuilder, in the case we want an item with the enchantment glow with no special effects.

Other notes:
Personally, there are things I really like about your ItemBuilder, but technically speaking it doesn't "build" anything. A builder class should not modify the resulting item as the methods are called, it should keep everything separate until a build() method is called, to which it will then take all stored variables and combine them into an ItemStack.

[CosimoTiger]

I specifically avoid making ItemBuilder a bloatware of countless variables that each have to be referenced and modified - my version takes less memory overall. The goal of the ItemBuilder is to allow chaining of ItemStack modifications, quickly modify existing ItemStacks and perhaps take different types of input (e.g. List and String[]). Additionally, I want this to be dependent on Bukkit's definition of ItemStack rather than having to change the variables in the ItemBuilder in the future.

I'm aware it's not necessarily a 'builder', I can't quite find a truer name, but I'm definitely not going to change the very useful function to fit a very close enough name.

[CosimoTiger]

Thank you for your contribution though! 😊