DATACMNS-534 - Add support to mark a persistent property as read only.

This commit introduces @ReadOnlyProperty to mark properties as not to be persisted. That trait is exposed via the newly added PersistentProperty.isWritable() which supersedes shallBePersisted(). Currently all non-transient property that are not annotated with @ReadOnlyProperty are considered writable.

Original pull request: #88.

src/main/java/org/springframework/data/annotation/ReadOnlyProperty.java

@@ -0,0 +1,33 @@
+/*
+ * Copyright 2014 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.data.annotation;
+
+import static java.lang.annotation.ElementType.*;
+
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+/**
+ * Marks a field to be {@literal read-only} for the mapping framework and therefore will not be persisted.
+ * 
+ * @author Christoph Strobl
+ * @since 1.9
+ */
+@Retention(RetentionPolicy.RUNTIME)
+@Target(value = { FIELD, METHOD, ANNOTATION_TYPE })
+public @interface ReadOnlyProperty {
+}