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/Handle-plugin-prefixes-using-Log4J-configuration.patch

@@ -15,7 +15,7 @@ This may cause additional prefixes to be disabled for plugins bypassing
 the plugin logger.
 
 diff --git a/pom.xml b/pom.xml
-index 183c3c4c8..c18a7f5ca 100644
+index ae42b1d66..6e4924fff 100644
 --- a/pom.xml
 +++ b/pom.xml
 @@ -0,0 +0,0 @@
@@ -28,7 +28,7 @@ index 183c3c4c8..c18a7f5ca 100644
          <dependency>
              <groupId>org.apache.logging.log4j</groupId>
 diff --git a/src/main/java/org/spigotmc/SpigotConfig.java b/src/main/java/org/spigotmc/SpigotConfig.java
-index b171bdfaa..0d827815c 100644
+index fc6cb9306..bd601333e 100644
 --- a/src/main/java/org/spigotmc/SpigotConfig.java
 +++ b/src/main/java/org/spigotmc/SpigotConfig.java
 @@ -0,0 +0,0 @@ public class SpigotConfig