Added 'generate-structure' setting support and WorldCreator property.

Fixes BUKKIT-655 and BUKKIT-592

By: Eric Stokes <fernferret@gmail.com>

paper-api/src/main/java/org/bukkit/World.java

@@ -761,6 +761,13 @@ public interface World extends PluginMessageRecipient {
      */
     public WorldType getWorldType();
 
+    /**
+     * Gets whether or not structures are being generated.
+     *
+     * @return True if structures are being generated.
+     */
+    public boolean canGenerateStructures();
+
     /**
      * Represents various map environment types that a world may be
      */

paper-api/src/main/java/org/bukkit/WorldCreator.java

@@ -14,6 +14,7 @@ public class WorldCreator {
     private World.Environment environment = World.Environment.NORMAL;
     private ChunkGenerator generator = null;
     private WorldType type = WorldType.NORMAL;
+    private boolean generateStructures = true;
 
     /**
      * Creates an empty WorldCreationOptions for the given world name
@@ -201,6 +202,26 @@ public class WorldCreator {
         return this;
     }
 
+    /**
+     * Sets whether or not worlds created or loaded with this creator will have structures.
+     *
+     * @return This object, for chaining
+     */
+    public WorldCreator generateStructures(boolean generate) {
+        this.generateStructures = generate;
+
+        return this;
+    }
+
+    /**
+     * Gets whether or not structures will be generated in the world.
+     *
+     * @return True if structures will be generated
+     */
+    public boolean generateStructures() {
+        return generateStructures;
+    }
+
     /**
      * Creates a world with the specified options.
      * <p>