Changed tooltips of table headings from Mootools to Bootstrap

http://joomlacode.org/gf/project/joomla/tracker/?action=TrackerItemEdit&tracker_item_id=31212

![tooltips](https://f.cloud.github.com/assets/744259/692442/0ce76948-dc26-11e2-8e4a-99920752b52e.png)

#### Testing instructions
Go to any list view, like ```Content``` >> ```Article Manager``` and compare the tooltips on the headings.