Add default constructor to IdentityCacheWrapper

Kryo is spending a lot of time during serialization handling a
NoSuchMethodException. By adding this default constructor we can skip
doing all that work.

commons/src/test/java/org/archive/util/IdentityCacheableWrapper.java

@@ -31,6 +31,9 @@ public class IdentityCacheableWrapper<K> implements IdentityCacheable {
     
     protected K wrapped; 
     
+    // For Kryo serialization
+    IdentityCacheableWrapper() { }
+
     public IdentityCacheableWrapper(String key, K wrapped) {
         super();
         this.wrapped = wrapped;