Modal fix

Makes off screen modals accessible by opening a non fixed window at the scroll offset position on screen. Fixes #87
From what I've seen, this is what vanilla foundation does. It opens the window at 100px offset from the top of your viewport unless its on mobile, then it opens it at 0px offset because the modal is off screen. 800px is the breakpoint at which the modal opens full screen. It's probably better to use a project wide media query module for this but no such module exists yet.