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/Use-asynchronous-Log4j-2-loggers.patch

@@ -5,7 +5,7 @@ Subject: [PATCH] Use asynchronous Log4j 2 loggers
 
 
 diff --git a/pom.xml b/pom.xml
-index 3d2065fd75..e01d95f17d 100644
+index 3d2065fd7..e01d95f17 100644
 --- a/pom.xml
 +++ b/pom.xml
 @@ -0,0 +0,0 @@
@@ -24,7 +24,7 @@ index 3d2065fd75..e01d95f17d 100644
              <artifactId>asm</artifactId>
 diff --git a/src/main/resources/log4j2.component.properties b/src/main/resources/log4j2.component.properties
 new file mode 100644
-index 0000000000..ee7c90784c
+index 000000000..ee7c90784
 --- /dev/null
 +++ b/src/main/resources/log4j2.component.properties
 @@ -0,0 +1 @@