Add a spring-boot-developer-tools sample

Add a sample application that demonstrates how the
`spring-boot-developer-tools` module can be used.

Closes gh-3082

spring-boot-samples/spring-boot-sample-developer-tools/src/main/java/demo/Message.java

@@ -0,0 +1,23 @@
+/*
+ * Copyright 2012-2015 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 demo;
+
+public class Message {
+
+	public static String MESSAGE = "Message";
+
+}