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/Add-ray-tracing-methods-to-LivingEntity.patch

@@ -6,7 +6,7 @@ Subject: [PATCH] Add ray tracing methods to LivingEntity
 
 diff --git a/src/main/java/com/destroystokyo/paper/block/TargetBlockInfo.java b/src/main/java/com/destroystokyo/paper/block/TargetBlockInfo.java
 new file mode 100644
-index 000000000..18a96dbb0
+index 00000000..18a96dbb
 --- /dev/null
 +++ b/src/main/java/com/destroystokyo/paper/block/TargetBlockInfo.java
 @@ -0,0 +0,0 @@
@@ -65,7 +65,7 @@ index 000000000..18a96dbb0
 +    }
 +}
 diff --git a/src/main/java/org/bukkit/entity/LivingEntity.java b/src/main/java/org/bukkit/entity/LivingEntity.java
-index adae86709..6b2002ceb 100644
+index 6e3284b2..9dc0d4ce 100644
 --- a/src/main/java/org/bukkit/entity/LivingEntity.java
 +++ b/src/main/java/org/bukkit/entity/LivingEntity.java
 @@ -0,0 +0,0 @@ public interface LivingEntity extends Attributable, Damageable, ProjectileSource