Move version command update checking to the implementation

This makes it easier for downstream projects (forks) to replace the
version fetching system with their own. It is as simple as implementing
an interface and overriding the default implementation of
org.bukkit.UnsafeValues#getVersionFetcher()

It also makes it easier for us to organize things like the version
history feature.

Lastly I have updated the paper implementation to check against the site
API rather than against jenkins.

Spigot-API-Patches/0105-ItemStack-getMaxItemUseDuration.patch

@@ -0,0 +1,28 @@
+From 4ff82e5af876626b15bd1e45fedb42381fc7c7a3 Mon Sep 17 00:00:00 2001
+From: Aikar <aikar@aikar.co>
+Date: Tue, 5 Jun 2018 22:59:50 -0400
+Subject: [PATCH] ItemStack#getMaxItemUseDuration
+
+Allows you to determine how long it takes to use a usable/consumable item
+
+diff --git a/src/main/java/org/bukkit/inventory/ItemStack.java b/src/main/java/org/bukkit/inventory/ItemStack.java
+index 9526cfe0..f129121e 100644
+--- a/src/main/java/org/bukkit/inventory/ItemStack.java
++++ b/src/main/java/org/bukkit/inventory/ItemStack.java
+@@ -603,5 +603,13 @@ public class ItemStack implements Cloneable, ConfigurationSerializable {
+     public String getI18NDisplayName() {
+         return Bukkit.getServer().getItemFactory().getI18NDisplayName(this);
+     }
++
++    public int getMaxItemUseDuration() {
++        if (type == null || type == Material.AIR || !type.isItem()) {
++            return 0;
++        }
++        // Requires access to NMS
++        return ensureServerConversions().getMaxItemUseDuration();
++    }
+     // Paper end
+ }
+-- 
+2.21.0
+