Refefine $.fn.position in terms of offsetTop/Left to work w/ shadow DOM

The default implementation of position seems to barf when things are in
the shadow DOM. This seems to be a suitable replacement that doesn’t.

src/space-pen-extensions.coffee

@@ -78,6 +78,11 @@ jQuery.event.remove = (elem, types, originalHandler, selector, mappedTypes) ->
     handler = HandlersByOriginalHandler.get(originalHandler) ? originalHandler
   JQueryEventRemove(elem, types, handler, selector, mappedTypes, RemoveEventListener if atom?.commands?)
 
+jQuery.fn.position = ->
+  top = @[0].offsetTop
+  left = @[0].offsetLeft
+  {top, left}
+
 tooltipDefaults =
   delay:
     show: 1000