Add Velocity IP forwarding support (#1557)

While Velocity supports BungeeCord-style IP forwarding, it is not secure. Users
have a lot of problems setting up firewalls or setting up plugins like IPWhitelist.
Further, the BungeeCord IP forwarding protocol still retains essentially its original
form, when there is brand new support for custom login plugin messages in 1.13.

Velocity's modern IP forwarding uses an HMAC-SHA256 code to ensure authenticity
of messages, is packed into a binary format that is smaller than BungeeCord's
forwarding, and is integrated into the Minecraft login process by using the 1.13
login plugin message packet.

Spigot-Server-Patches/Load-version-history-at-server-start.patch

@@ -5,12 +5,12 @@ Subject: [PATCH] Load version history at server start
 
 
 diff --git a/src/main/java/net/minecraft/server/DedicatedServer.java b/src/main/java/net/minecraft/server/DedicatedServer.java
-index 674609cad3..1a332909b2 100644
+index fe259e985..d9c6b1104 100644
 --- a/src/main/java/net/minecraft/server/DedicatedServer.java
 +++ b/src/main/java/net/minecraft/server/DedicatedServer.java
 @@ -0,0 +0,0 @@ public class DedicatedServer extends MinecraftServer implements IMinecraftServer
-             // Paper start
-             com.destroystokyo.paper.PaperConfig.init((File) options.valueOf("paper-settings"));
+                 return false;
+             }
              com.destroystokyo.paper.PaperConfig.registerCommands();
 +            com.destroystokyo.paper.VersionHistoryManager.INSTANCE.getClass(); // load version history now
              // Paper end