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-Cartographer-Treasure-Maps.patch

@@ -9,7 +9,7 @@ Also allow turning off treasure maps all together as they can eat up Map ID's
 which are limited in quantity.
 
 diff --git a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
-index 4892113a15..406bc611c1 100644
+index 4892113a1..406bc611c 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 {
@@ -28,7 +28,7 @@ index 4892113a15..406bc611c1 100644
 +    }
  }
 diff --git a/src/main/java/net/minecraft/server/VillagerTrades.java b/src/main/java/net/minecraft/server/VillagerTrades.java
-index eabbf29334..0fbaa8dd6d 100644
+index ff3f15eac..ae5ed782e 100644
 --- a/src/main/java/net/minecraft/server/VillagerTrades.java
 +++ b/src/main/java/net/minecraft/server/VillagerTrades.java
 @@ -0,0 +0,0 @@ public class VillagerTrades {