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/0107-Add-server-name-parameter.patch

@@ -1,28 +0,0 @@
-From 00dc73fe3a8769eb28d5bc2eb930d75ae7816654 Mon Sep 17 00:00:00 2001
-From: Martin Panzer <postremus1996@googlemail.com>
-Date: Sat, 28 May 2016 16:54:03 +0200
-Subject: [PATCH] Add server-name parameter
-
-
-diff --git a/src/main/java/org/bukkit/craftbukkit/Main.java b/src/main/java/org/bukkit/craftbukkit/Main.java
-index 7f5ea764d7..c5d5121fd9 100644
---- a/src/main/java/org/bukkit/craftbukkit/Main.java
-+++ b/src/main/java/org/bukkit/craftbukkit/Main.java
-@@ -136,6 +136,14 @@ public class Main {
-                         .defaultsTo(new File("paper.yml"))
-                         .describedAs("Yml file");
-                 // Paper end
-+
-+                // Paper start
-+                acceptsAll(asList("server-name"), "Name of the server")
-+                        .withRequiredArg()
-+                        .ofType(String.class)
-+                        .defaultsTo("Unknown Server")
-+                        .describedAs("Name");
-+                // Paper end
-             }
-         };
- 
--- 
-2.21.0
-