Improvements to Logging Warnings/Dupe Entities - Resolves #1544

1) Removed "Regen" mode of Dupe UUID resolver, forced safe.
Some servers who updated before we had safe mode added still had this value.

There's really no reason to keep this mode, as we've seen that vanilla
triggers this often and 99.9999999% of cases will be an actual duplicate
that needs to be deleted.

2) Made Vanilla Debug messages about dupe UUIDs and dupe uuid resolve messages
only show up if the debug.entities flag is on. This will stop server owners
from panicing from seeing these logs, and stop opening bug reports on this,
only for us to tell you "don't worry about it".

3) Avoid adding entities to world that are already added to world.

This can be triggered by anything that causes an entity to be added
to the world during the chunk load process, such as chunk conversions.

Issue #1544 was a case of this.

4) Removed debug warning about ExpiringMap.

Nothing more I know to do about this anyways. We recover from it,
stop warning to reduce noise of issues to us.

Spigot-Server-Patches/0339-Add-source-block-to-BlockPhysicsEvent.patch

@@ -1,14 +1,14 @@
-From df4ecee0af1df4edb57d94b00c33ead1d68ea27a Mon Sep 17 00:00:00 2001
+From 69f7ce35c27fc02b9c1f01c4b57fc48da48179b4 Mon Sep 17 00:00:00 2001
 From: Sotr <i@omc.hk>
 Date: Thu, 23 Aug 2018 16:14:12 +0800
 Subject: [PATCH] Add source block to BlockPhysicsEvent
 
 
 diff --git a/src/main/java/net/minecraft/server/World.java b/src/main/java/net/minecraft/server/World.java
-index 39175ea0ad..4426798c74 100644
+index a7dcfb4191..f713b0d3d0 100644
 --- a/src/main/java/net/minecraft/server/World.java
 +++ b/src/main/java/net/minecraft/server/World.java
-@@ -629,7 +629,7 @@ public abstract class World implements IEntityAccess, GeneratorAccess, IIBlockAc
+@@ -630,7 +630,7 @@ public abstract class World implements IEntityAccess, GeneratorAccess, IIBlockAc
                  // CraftBukkit start
                  CraftWorld world = ((WorldServer) this).getWorld();
                  if (world != null && !((WorldServer)this).stopPhysicsEvent) { // Paper