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/Configurable-Non-Player-Arrow-Despawn-Rate.patch

@@ -6,7 +6,7 @@ Subject: [PATCH] Configurable Non Player Arrow Despawn Rate
 Can set a much shorter despawn rate for arrows that players can not pick up.
 
 diff --git a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
-index 89556dc94a..98049567f4 100644
+index 89556dc94..98049567f 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 {
@@ -30,7 +30,7 @@ index 89556dc94a..98049567f4 100644
 +    }
  }
 diff --git a/src/main/java/net/minecraft/server/EntityArrow.java b/src/main/java/net/minecraft/server/EntityArrow.java
-index bc391812d3..b5b569ef95 100644
+index b50f996b6..531bb7f66 100644
 --- a/src/main/java/net/minecraft/server/EntityArrow.java
 +++ b/src/main/java/net/minecraft/server/EntityArrow.java
 @@ -0,0 +0,0 @@ public abstract class EntityArrow extends Entity implements IProjectile {