Fixes for StructureGenerationConfig

- Do not reset, again not for the API to enforce
- Add presets for "standard", "flat", and "none

Signed-off-by: Chris Sanders <zidane@spongepowered.org>

src/main/java/org/spongepowered/api/world/generation/config/structure/StructureGenerationConfig.java

@@ -34,8 +34,20 @@ import java.util.Optional;
 
 public interface StructureGenerationConfig {
 
+    static StructureGenerationConfig standard() {
+        return Sponge.game().factoryProvider().provide(Factory.class).standard();
+    }
+
+    static StructureGenerationConfig flat() {
+        return Sponge.game().factoryProvider().provide(Factory.class).flat();
+    }
+
+    static StructureGenerationConfig none() {
+        return Sponge.game().factoryProvider().provide(Factory.class).none();
+    }
+
     static Builder builder() {
-        return Sponge.game().builderProvider().provide(Builder.class).reset();
+        return Sponge.game().builderProvider().provide(Builder.class);
     }
 
     Optional<SpacedStructureConfig> stronghold();
@@ -54,4 +66,13 @@ public interface StructureGenerationConfig {
 
         Builder removeStructure(Structure structure);
     }
+
+    interface Factory {
+
+        StructureGenerationConfig standard();
+
+        StructureGenerationConfig flat();
+
+        StructureGenerationConfig none();
+    }
 }