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/0163-Add-more-Witch-API.patch

@@ -0,0 +1,57 @@
+From f3be0787b2990390ac5709f7069844505af7b986 Mon Sep 17 00:00:00 2001
+From: BillyGalbreath <Blake.Galbreath@GMail.com>
+Date: Fri, 12 Oct 2018 03:47:26 -0500
+Subject: [PATCH] Add more Witch API
+
+
+diff --git a/src/main/java/org/bukkit/entity/Witch.java b/src/main/java/org/bukkit/entity/Witch.java
+index aa88aede..cd8d0a20 100644
+--- a/src/main/java/org/bukkit/entity/Witch.java
++++ b/src/main/java/org/bukkit/entity/Witch.java
+@@ -2,8 +2,43 @@ package org.bukkit.entity;
+ 
+ import com.destroystokyo.paper.entity.RangedEntity;
+ 
++// Paper start
++import org.bukkit.inventory.ItemStack;
++import org.jetbrains.annotations.Nullable;
++// Paper end
++
+ /**
+  * Represents a Witch
+  */
+ public interface Witch extends Raider, RangedEntity { // Paper
++    // Paper start
++    /**
++     * Check if Witch is drinking a potion
++     *
++     * @return True if drinking a potion
++     */
++    boolean isDrinkingPotion();
++
++    /**
++     * Get time remaining (in ticks) the Witch is drinking a potion
++     *
++     * @return Time remaining (in ticks)
++     */
++    int getPotionUseTimeLeft();
++
++    /**
++     * Get the potion the Witch is drinking
++     *
++     * @return The potion the witch is drinking
++     */
++    @Nullable
++    ItemStack getDrinkingPotion();
++
++    /**
++     * Set the potion the Witch should drink
++     *
++     * @param potion Potion to drink
++     */
++    void setDrinkingPotion(@Nullable ItemStack potion);
++    // Paper end
+ }
+-- 
+2.21.0
+