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/boot/src/main/java/sample/config/HttpSessionConfig.java

@@ -16,8 +16,8 @@
 package sample.config;
 
 import org.springframework.session.data.redis.config.annotation.web.http.*;
+import org.springframework.session.redis.embedded.EnableEmbeddedRedis;
 
-import sample.EnableEmbeddedRedis;
 
 @EnableEmbeddedRedis
 // tag::class[]