structure predicate stuff + fix sunflower plains trees

src/main/java/com/terraforged/fm/structure/StructureManager.java

@@ -0,0 +1,28 @@
+package com.terraforged.fm.structure;
+
+import com.terraforged.fm.predicate.FeaturePredicate;
+import net.minecraft.world.gen.feature.structure.Structure;
+
+import java.util.HashMap;
+import java.util.Map;
+
+public class StructureManager {
+
+    private final Map<String, FeaturePredicate> predicates = new HashMap<>();
+
+    public void register(Structure<?> structure, FeaturePredicate predicate) {
+        register(structure.getStructureName(), predicate);
+    }
+
+    public void register(String structureName, FeaturePredicate predicate) {
+        predicates.put(structureName, predicate);
+    }
+
+    public FeaturePredicate getPredicate(Structure<?> structure) {
+        return getPredicate(structure.getStructureName());
+    }
+
+    public FeaturePredicate getPredicate(String structureName) {
+        return predicates.getOrDefault(structureName, FeaturePredicate.ALLOW);
+    }
+}