Event handler refactoring (Using the on() method)

Replaced event handler aliases (click, mouseenter, …) with the on() method which is the preferred method for binding events since jQuery 1.7.

Also, now that developers are able to create custom jQuery 2 builds without aliases/shortcuts, Zoom wouldn't break if using on(). :)

The only drawback I see is that Zoom now requires jQuery >=1.7. But, is this a real problem nowadays?