INT-2964 - Make Spring Integration buildable with JDK8

For reference see: https://jira.springsource.org/browse/INT-2964


* `<li></li>` should be wrapped in `<ul></ul>`
* wrap code snippets in {@code myCode()}
* change `<code>false</false>` to `<code>false</code>`
* `<p/>` should be `<p>`
* `<emphasis>` should be `<em>`
* Mockito-all dependency causes JavaDoc error. Change dependency to Mockito-Core.
* In Java 8 there seems to be a timing issue coming up with test:

`org.springframework.integration_.mbeanexporterhelper.Int2307Tests#testInt2307_DefaultMBeanExporter()`

* Adding Thread.sleep(500) seems to help (But not completely solve test fairlures). May need to revisit with more recent JDK8 builds. If setting lower values, intermittent test failures start to appear.