Fix tooltip positioning with regards to viewports

The getPosition function was simplified with a new function,
getViewportBounds, was added to specifically
tackle the cases where we’re looking for the viewport bounds.

‘absolute’ and ‘fixed’ tooltips are now matched against the screen
where other ones are made to fit inside the viewport element.
Thanks for sharing!  Since I'm new to all this that's priceless when you guys share information like this!

I have a bunch of meetings in the afternoon, but I definitely wouldn't mind changing it to `$(document.body)` later tonight!