Do not use worldgen executor for api profile completions

We cannot put blocking network I/O onto the worldgen threads,
this will crash the server if it stalls

patches/server/0182-getPlayerUniqueId-API.patch

@@ -0,0 +1,40 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Aikar <aikar@aikar.co>
+Date: Thu, 22 Mar 2018 01:40:24 -0400
+Subject: [PATCH] getPlayerUniqueId API
+
+Gets the unique ID of the player currently known as the specified player name
+In Offline Mode, will return an Offline UUID
+
+This is a more performant way to obtain a UUID for a name than loading an OfflinePlayer
+
+diff --git a/src/main/java/org/bukkit/craftbukkit/CraftServer.java b/src/main/java/org/bukkit/craftbukkit/CraftServer.java
+index 7e3631a75a2221955199f746e9b8f406a744121a..4950f11c12f29cb363acd639c16c4aa8efafdd17 100644
+--- a/src/main/java/org/bukkit/craftbukkit/CraftServer.java
++++ b/src/main/java/org/bukkit/craftbukkit/CraftServer.java
+@@ -1704,6 +1704,25 @@ public final class CraftServer implements Server {
+         return recipients.size();
+     }
+ 
++    // Paper start
++    @Nullable
++    public UUID getPlayerUniqueId(String name) {
++        Player player = Bukkit.getPlayerExact(name);
++        if (player != null) {
++            return player.getUniqueId();
++        }
++        GameProfile profile;
++        // Only fetch an online UUID in online mode
++        if (io.papermc.paper.configuration.GlobalConfiguration.get().proxies.isProxyOnlineMode()) {
++            profile = console.getProfileCache().get(name).orElse(null);
++        } else {
++            // Make an OfflinePlayer using an offline mode UUID since the name has no profile
++            profile = new GameProfile(UUID.nameUUIDFromBytes(("OfflinePlayer:" + name).getBytes(Charsets.UTF_8)), name);
++        }
++        return profile != null ? profile.getId() : null;
++    }
++    // Paper end
++
+     @Override
+     @Deprecated
+     public OfflinePlayer getOfflinePlayer(String name) {