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-Server-Patches/Make-shield-blocking-delay-configurable.patch

@@ -5,7 +5,7 @@ Subject: [PATCH] Make shield blocking delay configurable
 
 
 diff --git a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
-index fe9415b1de..ce17447faf 100644
+index fe9415b1d..ce17447fa 100644
 --- a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
 +++ b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
 @@ -0,0 +0,0 @@ public class PaperWorldConfig {
@@ -19,7 +19,7 @@ index fe9415b1de..ce17447faf 100644
 +    }
  }
 diff --git a/src/main/java/net/minecraft/server/EntityLiving.java b/src/main/java/net/minecraft/server/EntityLiving.java
-index 8642040786..be60f35de1 100644
+index fd8e625ff..c22e8bd17 100644
 --- a/src/main/java/net/minecraft/server/EntityLiving.java
 +++ b/src/main/java/net/minecraft/server/EntityLiving.java
 @@ -0,0 +0,0 @@ public abstract class EntityLiving extends Entity {
@@ -48,7 +48,7 @@ index 8642040786..be60f35de1 100644
 +    // Paper end
  }
 diff --git a/src/main/java/org/bukkit/craftbukkit/entity/CraftLivingEntity.java b/src/main/java/org/bukkit/craftbukkit/entity/CraftLivingEntity.java
-index 42cc158824..513b3fac7f 100644
+index 42cc15882..513b3fac7 100644
 --- a/src/main/java/org/bukkit/craftbukkit/entity/CraftLivingEntity.java
 +++ b/src/main/java/org/bukkit/craftbukkit/entity/CraftLivingEntity.java
 @@ -0,0 +0,0 @@ public class CraftLivingEntity extends CraftEntity implements LivingEntity {