Display release notes on separate pages for performance reasons

Right now all release notes are rendered when displaying the extension page. Several extensions calls jira.xwiki.org using the jira macro and as more releases are done the page loads slower and slower. We should instead display a link to release notes and have a separate generic page to display release notes.

Several other ideas:

• Reimplement the RN section as a LiveTable
• Offer an extension point (UIXP or XClass) so that other apps can provide a more sophisticated RN app. The idea would be for the RN App to implement that extension point.