Adding a scrollOffset option to the settings for fixed headers

I'm using Joyride on an application with a fixed header, and needed to be able to offset the ```scrollTop``` so that when ```scroll``` is set to ```true```, tips that are at the top of the main container wouldn't be scrolled to (underneath the fixed header). I added a ```scrollOffset``` option to the settings, which is defaulted to ```0```. I thought this would be a pretty common scenario that others would benefit from.