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/0173-Annotation-Test-changes.patch

@@ -0,0 +1,32 @@
+From 1a26c0d087846c0ff615263216505475184cf2c4 Mon Sep 17 00:00:00 2001
+From: Shane Freeder <theboyetronic@gmail.com>
+Date: Sun, 17 Mar 2019 23:04:30 +0000
+Subject: [PATCH] Annotation Test changes
+
+
+diff --git a/src/test/java/org/bukkit/AnnotationTest.java b/src/test/java/org/bukkit/AnnotationTest.java
+index cc6b6e20..328a5a16 100644
+--- a/src/test/java/org/bukkit/AnnotationTest.java
++++ b/src/test/java/org/bukkit/AnnotationTest.java
+@@ -40,7 +40,17 @@ public class AnnotationTest {
+         "org/bukkit/util/io/Wrapper",
+         "org/bukkit/plugin/java/PluginClassLoader",
+         // Generic functional interface
+-        "org/bukkit/util/Consumer"
++        "org/bukkit/util/Consumer",
++        // Paper start
++        // Timings history is broken in terms of nullability due to guavas Function defining that the param is NonNull
++        "co/aikar/timings/TimingHistory$2",
++        "co/aikar/timings/TimingHistory$2$1",
++        "co/aikar/timings/TimingHistory$2$1$1",
++        "co/aikar/timings/TimingHistory$2$1$2",
++        "co/aikar/timings/TimingHistory$3",
++        "co/aikar/timings/TimingHistory$4",
++        "co/aikar/timings/TimingHistoryEntry$1"
++        // Paper end
+     };
+ 
+     @Test
+-- 
+2.21.0
+