More use of Visitor pattern - allowing iteration over all cards in the game without allocating a temporary collection.

forge-core/src/main/java/forge/util/Visitor.java

@@ -0,0 +1,11 @@
+package forge.util;
+
+public abstract class Visitor<T> {
+    public abstract void visit(T object);
+
+    public void visitAll(Iterable<? extends T> objects) {
+        for (T obj : objects) {
+            visit(obj);
+        }
+    }
+}