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/0138-String-based-Action-Bar-API.patch

@@ -1,69 +0,0 @@
-From fc25517cebc592f17213a25323f0954d9e540e5d Mon Sep 17 00:00:00 2001
-From: Aikar <aikar@aikar.co>
-Date: Tue, 27 Dec 2016 15:02:42 -0500
-Subject: [PATCH] String based Action Bar API
-
-
-diff --git a/src/main/java/net/minecraft/server/MCUtil.java b/src/main/java/net/minecraft/server/MCUtil.java
-index 3448b5588e..d7dc516e4a 100644
---- a/src/main/java/net/minecraft/server/MCUtil.java
-+++ b/src/main/java/net/minecraft/server/MCUtil.java
-@@ -2,6 +2,7 @@ package net.minecraft.server;
- 
- import com.destroystokyo.paper.block.TargetBlockInfo;
- import com.google.common.util.concurrent.ThreadFactoryBuilder;
-+import org.apache.commons.lang.exception.ExceptionUtils;
- import org.bukkit.Location;
- import org.bukkit.block.BlockFace;
- import org.bukkit.craftbukkit.CraftWorld;
-@@ -24,6 +25,24 @@ public final class MCUtil {
- 
-     private MCUtil() {}
- 
-+    /**
-+     * Quickly generate a stack trace for current location
-+     *
-+     * @return Stacktrace
-+     */
-+    public static String stack() {
-+        return ExceptionUtils.getFullStackTrace(new Throwable());
-+    }
-+
-+    /**
-+     * Quickly generate a stack trace for current location with message
-+     *
-+     * @param str
-+     * @return Stacktrace
-+     */
-+    public static String stack(String str) {
-+        return ExceptionUtils.getFullStackTrace(new Throwable(str));
-+    }
- 
-     public static boolean isMainThread() {
-         return MinecraftServer.getServer().isMainThread();
-diff --git a/src/main/java/org/bukkit/craftbukkit/entity/CraftPlayer.java b/src/main/java/org/bukkit/craftbukkit/entity/CraftPlayer.java
-index 06db4a8f04..37e9c86375 100644
---- a/src/main/java/org/bukkit/craftbukkit/entity/CraftPlayer.java
-+++ b/src/main/java/org/bukkit/craftbukkit/entity/CraftPlayer.java
-@@ -214,6 +214,18 @@ public class CraftPlayer extends CraftHumanEntity implements Player {
-     }
- 
-     // Paper start
-+    @Override
-+    public void sendActionBar(String message) {
-+        if (getHandle().playerConnection == null || message == null || message.isEmpty()) return;
-+        getHandle().playerConnection.sendPacket(new PacketPlayOutChat(new net.minecraft.server.ChatComponentText(message), net.minecraft.server.ChatMessageType.GAME_INFO));
-+    }
-+
-+    @Override
-+    public void sendActionBar(char alternateChar, String message) {
-+        if (message == null || message.isEmpty()) return;
-+        sendActionBar(org.bukkit.ChatColor.translateAlternateColorCodes(alternateChar, message));
-+    }
-+
-     @Override
-     public void setPlayerListHeaderFooter(BaseComponent[] header, BaseComponent[] footer) {
-          if (header != null) {
--- 
-2.21.0
-