Move Embedded Redis classes to org.springframework.session.redis.embedded

This prevents the embedded redis from being picked up in ComponentScan
in any of the samples unless the @EnableEmebeddedRedis annotation is used.

Polish gh-184

samples/httpsession/src/main/java/sample/Config.java

@@ -18,6 +18,8 @@ package sample;
 import org.springframework.context.annotation.Bean;
 import org.springframework.data.redis.connection.jedis.JedisConnectionFactory;
 import org.springframework.session.data.redis.config.annotation.web.http.EnableRedisHttpSession;
+import org.springframework.session.redis.embedded.EnableEmbeddedRedis;
+import org.springframework.session.redis.embedded.RedisServerPort;
 
 // tag::class[]
 @EnableEmbeddedRedis // <1>