Polish cache sample

Update single cache sample with all supported cache providers. Add README
to shortly explain how to get started with them.

See gh-2633

spring-boot-samples/spring-boot-sample-cache/src/main/java/sample/SampleCacheApplication.java

@@ -0,0 +1,63 @@
+/*
+ * 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 sample;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.CommandLineRunner;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+import org.springframework.boot.builder.SpringApplicationBuilder;
+import org.springframework.cache.CacheManager;
+import org.springframework.cache.annotation.EnableCaching;
+import org.springframework.scheduling.annotation.EnableScheduling;
+import org.springframework.stereotype.Component;
+
+@EnableCaching
+@EnableScheduling
+@SpringBootApplication
+public class SampleCacheApplication {
+
+	private static final Logger logger = LoggerFactory.getLogger(SampleCacheApplication.class);
+
+	public static void main(String[] args) {
+		new SpringApplicationBuilder()
+				.sources(SampleCacheApplication.class)
+				.profiles("app")
+				.run(args);
+	}
+
+	@Component
+	static class CacheManagerCheck implements CommandLineRunner {
+
+		private final CacheManager cacheManager;
+
+		@Autowired
+		CacheManagerCheck(CacheManager cacheManager) {
+			this.cacheManager = cacheManager;
+		}
+
+		@Override
+		public void run(String... strings) throws Exception {
+			logger.info("\n\n" + "=========================================================\n"
+					+ "Using cache manager: " + this.cacheManager.getClass().getName() + "\n"
+					+ "=========================================================\n\n");
+		}
+	}
+
+}