Replace Skin id by Skin uuid

[TheRocketOff]

Hello,

I noticed a problem in the plugin.

Indeed, the ids are no longer functional.

So I propose to replace the ids by the uuids with this code:

Replace private static final String MINESKIN_API = "https://api.mineskin.org/get/id/"; in MineSkinFetcher by private static final String MINESKIN_API = "https://api.mineskin.org/get/uuid/"

And change the name of the method fecthSkinFromIdAsync to fetchSkinFromUniqueIdAsync And change int id to UUID uuid

[vytskalt]

Why not create a PR for this?