Change ItemPrototype.tier to be of type int

[Therenas]

This is probably a bit nitpicky, but I would feel better if the .tier attribute on ItemPrototypes was an interger and not a float. It seems like that would make more sense and reduce the surface for error, especially across mods. Unless there is a reason for it to be a float that I'm not aware of.

[Bilka]

What is the use case of this change?

[Therenas]

Makes me not have to worry about some mod setting a tier of 0.001256 and having to have code to deal with it. Makes it simpler if I can assume that that number will always be an int. Just a small quality of life improvement, and it makes the modding interface cleaner I guess.

[Bilka]

Okay, changed for the next version.