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/RangedEntity-API.patch

@@ -79,7 +79,7 @@ index c4385429..d23226cc 100644
      /**
       * Represents the base color that the llama has.
 diff --git a/src/main/java/org/bukkit/entity/Skeleton.java b/src/main/java/org/bukkit/entity/Skeleton.java
-index 2ac30c0f..d42a4e12 100644
+index 16b12938..1c367f78 100644
 --- a/src/main/java/org/bukkit/entity/Skeleton.java
 +++ b/src/main/java/org/bukkit/entity/Skeleton.java
 @@ -0,0 +0,0 @@ package org.bukkit.entity;
@@ -144,7 +144,7 @@ index 3bc332ee..426d3693 100644
 +public interface Wither extends Monster, Boss, RangedEntity { // Paper
  }
 diff --git a/src/main/java/org/bukkit/inventory/ItemStack.java b/src/main/java/org/bukkit/inventory/ItemStack.java
-index 72e268c1..76da06d1 100644
+index 690abbba..6d18de76 100644
 --- a/src/main/java/org/bukkit/inventory/ItemStack.java
 +++ b/src/main/java/org/bukkit/inventory/ItemStack.java
 @@ -0,0 +0,0 @@ import org.jetbrains.annotations.NotNull;