Added scrollEvents parameter to disable animation on scroll

Added a scrollEvents parameter that can be set by the user.  If set to
false, plugin will ignore scroll events and will not animate when they
are detected such as when the scroll wheel is moved or someone scrolls
on a mobile device.  Is useful when you want to only scroll using the
moveUp and moveDown methods.  I have tested this on various browsers and mobile devices and seems to be working well, but I would appreciate someone else looking at it to make sure I did not miss anything.  

I'm using this on one of my projects and figured someone might find it useful.