Upgrade page tabs

A few months ago, the team discussed adding functionality to the tab regions used on the documentation pages.

We agreed that it would be useful if the tabs could be synchonised, so that if a reader was looking at tabs containing Java code, then all the tabs on the page would be set to display code in Java.

Dan Allen at OpenDevise has rewritten the Asciidoctor tab extension to support the synchronisation function.

This Jira will track the work to incorporate the new extension site-wide.