Add config options to paper.yml for Async Chunks and Shared Host Overrides

Shared Hosts have been concerned over the increased CPU usage that Async Chunks
has introduced. We understand that shared hosts can't allow 1 client
to abuse the systme resources depriving other servers of cpu time, so we've
added some configs to allow hosts to force some settings.

Hosts, you may set the following SYSTEM ENVIRONMENT VARIABLES (NOT JVM FLAGS)
to change some behavior:

PAPER_ASYNC_CHUNKS_SHARED_HOST_GEN=1   - Enable Single Threaded World Generation (capping CPU Usage
PAPER_ASYNC_CHUNKS_SHARED_HOST_GEN=2   - Disable Async Chunk Generation - Please do not do this!!!
  - Minecraft is moving towards asynchronousm per-world chunk generation itself. You need to prepare
  - for this, so please do not disable async chunk generation.

PAPER_ASYNC_CHUNKS_SHARED_HOST_LOAD=#  - Where # is Maximum number of threads to use on Chunk Loading
  - This is a max, so your end user can reduce it more too. I suggest no lower than 2. Minimum is 1.
  - These are usually much faster request, so outside of loading entire worlds, They usually do not
  - get as much load. Paperby default uses CPU Core count * 1.5, so this may default to a higher value
  - on shared host and you should override it with this value to say 2-4.

These settings will override your clients paper.yml options. Set as a system wide environment
variable to ensure all Paper clients respect your resource usage desires.

Resolves #1520

Spigot-Server-Patches/Paper-config-files.patch

@@ -6,7 +6,7 @@ Subject: [PATCH] Paper config files
 
 diff --git a/src/main/java/com/destroystokyo/paper/PaperCommand.java b/src/main/java/com/destroystokyo/paper/PaperCommand.java
 new file mode 100644
-index 000000000..961966e16
+index 0000000000..961966e169
 --- /dev/null
 +++ b/src/main/java/com/destroystokyo/paper/PaperCommand.java
 @@ -0,0 +0,0 @@
@@ -249,7 +249,7 @@ index 000000000..961966e16
 +}
 diff --git a/src/main/java/com/destroystokyo/paper/PaperConfig.java b/src/main/java/com/destroystokyo/paper/PaperConfig.java
 new file mode 100644
-index 000000000..104abab84
+index 0000000000..92e44befe0
 --- /dev/null
 +++ b/src/main/java/com/destroystokyo/paper/PaperConfig.java
 @@ -0,0 +0,0 @@
@@ -313,7 +313,7 @@ index 000000000..104abab84
 +        commands.put("paper", new PaperCommand("paper"));
 +
 +        version = getInt("config-version", 14);
-+        set("config-version", 14);
++        set("config-version", 15);
 +        readConfig(PaperConfig.class, null);
 +    }
 +
@@ -432,7 +432,7 @@ index 000000000..104abab84
 +}
 diff --git a/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
 new file mode 100644
-index 000000000..a73865739
+index 0000000000..a738657394
 --- /dev/null
 +++ b/src/main/java/com/destroystokyo/paper/PaperWorldConfig.java
 @@ -0,0 +0,0 @@
@@ -504,7 +504,7 @@ index 000000000..a73865739
 +    }
 +}
 diff --git a/src/main/java/net/minecraft/server/DedicatedServer.java b/src/main/java/net/minecraft/server/DedicatedServer.java
-index 8b3988fc0..d8535fdd9 100644
+index 8b3988fc0a..d8535fdd9e 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
@@ -519,7 +519,7 @@ index 8b3988fc0..d8535fdd9 100644
              DedicatedServer.LOGGER.info("Generating keypair");
              this.a(MinecraftEncryption.b());
 diff --git a/src/main/java/net/minecraft/server/Entity.java b/src/main/java/net/minecraft/server/Entity.java
-index 709b28d78..4ba748ae2 100644
+index 3c7537d013..ffaa425ec8 100644
 --- a/src/main/java/net/minecraft/server/Entity.java
 +++ b/src/main/java/net/minecraft/server/Entity.java
 @@ -0,0 +0,0 @@ public abstract class Entity implements INamableTileEntity, ICommandListener {
@@ -536,7 +536,7 @@ index 709b28d78..4ba748ae2 100644
      public boolean impulse;
      public int portalCooldown;
 diff --git a/src/main/java/net/minecraft/server/EntityTypes.java b/src/main/java/net/minecraft/server/EntityTypes.java
-index c6434ec37..17bfa356f 100644
+index c6434ec371..17bfa356f1 100644
 --- a/src/main/java/net/minecraft/server/EntityTypes.java
 +++ b/src/main/java/net/minecraft/server/EntityTypes.java
 @@ -0,0 +0,0 @@ package net.minecraft.server;
@@ -560,7 +560,7 @@ index c6434ec37..17bfa356f 100644
 +    // Paper end
  }
 diff --git a/src/main/java/net/minecraft/server/World.java b/src/main/java/net/minecraft/server/World.java
-index ed77641e4..f381e23be 100644
+index ed77641e46..f381e23beb 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
@@ -581,7 +581,7 @@ index ed77641e4..f381e23be 100644
          this.world = new CraftWorld((WorldServer) this, gen, env);
          this.ticksPerAnimalSpawns = this.getServer().getTicksPerAnimalSpawns(); // CraftBukkit
 diff --git a/src/main/java/org/bukkit/craftbukkit/CraftServer.java b/src/main/java/org/bukkit/craftbukkit/CraftServer.java
-index e28ce05fb..e659f3f33 100644
+index e28ce05fb9..e659f3f339 100644
 --- a/src/main/java/org/bukkit/craftbukkit/CraftServer.java
 +++ b/src/main/java/org/bukkit/craftbukkit/CraftServer.java
 @@ -0,0 +0,0 @@ public final class CraftServer implements Server {
@@ -636,7 +636,7 @@ index e28ce05fb..e659f3f33 100644
 +    // Paper end
  }
 diff --git a/src/main/java/org/bukkit/craftbukkit/Main.java b/src/main/java/org/bukkit/craftbukkit/Main.java
-index 4a998593b..e354245f7 100644
+index 4a998593bd..e354245f73 100644
 --- a/src/main/java/org/bukkit/craftbukkit/Main.java
 +++ b/src/main/java/org/bukkit/craftbukkit/Main.java
 @@ -0,0 +0,0 @@ public class Main {
@@ -655,7 +655,7 @@ index 4a998593b..e354245f7 100644
          };
  
 diff --git a/src/main/java/org/spigotmc/SpigotWorldConfig.java b/src/main/java/org/spigotmc/SpigotWorldConfig.java
-index 95f7a9587..87bc8e2d9 100644
+index 95f7a9587a..87bc8e2d9c 100644
 --- a/src/main/java/org/spigotmc/SpigotWorldConfig.java
 +++ b/src/main/java/org/spigotmc/SpigotWorldConfig.java
 @@ -0,0 +0,0 @@ public class SpigotWorldConfig