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/0096-Location.isChunkLoaded-API.patch

@@ -0,0 +1,21 @@
+From 947a4656a70657d309ba4c02c36a3b5277d5d4c6 Mon Sep 17 00:00:00 2001
+From: Aikar <aikar@aikar.co>
+Date: Mon, 30 Apr 2018 19:27:31 -0400
+Subject: [PATCH] Location.isChunkLoaded() API
+
+
+diff --git a/src/main/java/org/bukkit/Location.java b/src/main/java/org/bukkit/Location.java
+index 44e3bca6..6021e672 100644
+--- a/src/main/java/org/bukkit/Location.java
++++ b/src/main/java/org/bukkit/Location.java
+@@ -533,6 +533,7 @@ public class Location implements Cloneable, ConfigurationSerializable {
+         return this;
+     }
+ 
++    public boolean isChunkLoaded() { return this.getWorld().isChunkLoaded(locToBlock(x) >> 4, locToBlock(z) >> 4); } // Paper
+     @Override
+     public boolean equals(Object obj) {
+         if (obj == null) {
+-- 
+2.21.0
+