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/0107-Make-shield-blocking-delay-configurable.patch

@@ -0,0 +1,33 @@
+From 8ed3dc7a4e8ac87e1972ef34e9b3896603fb69d4 Mon Sep 17 00:00:00 2001
+From: BillyGalbreath <Blake.Galbreath@GMail.com>
+Date: Sat, 16 Jun 2018 01:17:39 -0500
+Subject: [PATCH] Make shield blocking delay configurable
+
+
+diff --git a/src/main/java/org/bukkit/entity/LivingEntity.java b/src/main/java/org/bukkit/entity/LivingEntity.java
+index ffbf3d7a..e08dfe17 100644
+--- a/src/main/java/org/bukkit/entity/LivingEntity.java
++++ b/src/main/java/org/bukkit/entity/LivingEntity.java
+@@ -523,5 +523,19 @@ public interface LivingEntity extends Attributable, Damageable, ProjectileSource
+      * @param arrows Number of arrows to stick in this entity
+      */
+     void setArrowsStuck(int arrows);
++
++    /**
++     * Get the delay (in ticks) before blocking is effective for this entity
++     *
++     * @return Delay in ticks
++     */
++    int getShieldBlockingDelay();
++
++    /**
++     * Set the delay (in ticks) before blocking is effective for this entity
++     *
++     * @param delay Delay in ticks
++     */
++    void setShieldBlockingDelay(int delay);
+     // Paper end
+ }
+-- 
+2.21.0
+