Added 2 new options for XPStorer, and the ability to set the block to
air, making it occur whenever you right click.
You can require a glass bottle for every xp bottle, which goes in nicely
with the no block part, as you can right click a glass bottle anywhere
to store XP in it.
Also, you can now set how much XP each bottle is worth, so you can make
them very expensive to create, or very cheap.
The algorithm is also now a bit better, returning the correct XP etc.
Also, messages are now displayed.
Fixed it erroring with no block.