Popup doesn't appear in IE

In IE (tested on IE11 / Edge), the popups are not appearing because the positioning code is not working.
This comes down to IE not supplying the window.scrollX / window.scrollY values (return undefined).

The fix is to make the following edits to views_popup.js:

• replace all references to window.scrollX with (window.scrollX || window.pageXOffset)
• replace all references to window.scrollY with (window.scrollY || window.pageYOffset)