Revert "properly correct the CSS to show the red number per tooltip: now the red circle is bigger and fits each number easily."

This reverts commit 6e64d8c87a3062c51c81b15fb76b276275efb25e.

That commit changed the red number styling to suit my browsers but for some unidentified reason all browsers were rendering incorrectly - the next night, after a complete machine crash (hardware freeze) and reboot the edited styling is wrong, as it was on a freind's machine (OS/X) -- for which I had no explanation at the time. Apparently something very odd happened on the local dev box there.
- added preliminary example to showcase custom actions when overlay is clicked.

- user callbacks introExitCallback and introCompleteCallback now are called with a 'reason' parameter, which is an object containing information about which action/event triggered the callback.

- always call _exitIntro() AFTER the user callbacks have been invoked: hence _exitIntro is the very last action performed by IntroJS when the demonstration terminates.