"Unequippable" rename

[DinizSa]

From chatgpt3 the definition of “Unequippable” is: "something cannot be equipped or used for its intended purpose".
However in the contract the variable "unequippable" is used to determine if an item can be unequipped, which might lead to confusion.

I would like to suggest a rename of this variable. Maybe "persistent" or “permanent” would be a better fit.

[ogarciarevett]

Renaming the function facets, means that anyone with the new version, will have an Error in their game/system that's using the inventory.

As breaking change I'll put this over our list for the next major version