IE8 bug fixes, code cleaning

- IE8 defaults to the handlebar.js cart template in the ajax modal and drawer because it doesn't support jQuery's `.load` function
- [IE8 fires a resize event all the time](http://stackoverflow.com/questions/1852751/window-resize-event-firing-in-internet-explorer), so now it's excluded for updating the modal size
- Took window scroll into account when aligning modal close button
- IE8 modal now has an overlay you can see
- Resize and onorientationchange are only initialized once
- Added modal overlay and close button to the setup function where they belong
- Transition mixin no longer breaks with multiple arguments, just use quotes when passing in the transition
  - E.g. `@include transition('background-color 100ms ease-in-out, margin 100ms ease-in-out');`