30599 bc break tabs

This is a propsed fix for http://joomlacode.org/gf/project/joomla/tracker/?action=TrackerItemEdit&tracker_item_id=30599

As the API was modified for JHtmlBootstrap::startPane and ::addPanel, the change reverts this back, and introduces new methods: startTabset, endTabSet, addTab and endTab. This new methods implements all the changes that were introduced recently in J 3.1, w/o interfering with pre-existing methods.

Where needed throughout the CMS, calls to JHtmlBootstrap::startPane have been changed to JHtmlBootstrap::startTabSet. Same for endPane, addPanel and endPanel.

Note that tabs html and javascript is now output through JLayout, so the tabs html and javascript can be overriden in templates.