INT-3154 Use SPR Javadoc Stylesheet

Use the Spring Framework stylesheet for javadocs.

Fix 3 missing package-info files.

(Aside: remove cache-sessions from 2 @Ignored test case configuration files).

spring-integration-core/src/main/java/org/springframework/integration/channel/registry/package-info.java

@@ -0,0 +1,4 @@
+/**
+ * Provides classes representing channel registries.
+ */
+package org.springframework.integration.channel.registry;

spring-integration-core/src/main/java/org/springframework/integration/transaction/package-info.java

@@ -0,0 +1,5 @@
+/**
+ * Provides classes supporting the use of transactions and
+ * pseudo transactions in Spring Integration applications.
+ */
+package org.springframework.integration.transaction;