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-file/src/main/java/org/springframework/integration/file/test/package-info.java

@@ -0,0 +1,5 @@
+/**
+ * Provides classes used to support common test cases in modules
+ * that are dependent on the file module.
+ */
+package org.springframework.integration.file.test;