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/Prevent-Mob-AI-Rules-from-Loading-Chunks.patch

@@ -5,7 +5,7 @@ Subject: [PATCH] Prevent Mob AI Rules from Loading Chunks
 
 
 diff --git a/src/main/java/net/minecraft/server/Chunk.java b/src/main/java/net/minecraft/server/Chunk.java
-index debf47d9fd..01244c1d37 100644
+index b8d87beae6..300c54c806 100644
 --- a/src/main/java/net/minecraft/server/Chunk.java
 +++ b/src/main/java/net/minecraft/server/Chunk.java
 @@ -0,0 +0,0 @@ public class Chunk implements IChunkAccess {
@@ -84,7 +84,7 @@ index 800e0046a8..bfa6c2eef8 100644
      }
  }
 diff --git a/src/main/java/net/minecraft/server/World.java b/src/main/java/net/minecraft/server/World.java
-index 0c42d042b1..e52e4bb458 100644
+index af7cbb5fcf..a2559f0c19 100644
 --- a/src/main/java/net/minecraft/server/World.java
 +++ b/src/main/java/net/minecraft/server/World.java
 @@ -0,0 +0,0 @@ public abstract class World implements IEntityAccess, GeneratorAccess, IIBlockAc