[FIX] excessive horizontal and vertical offsetting of edition button on images in webkit browsers

Manually adding margins to offsets was necessary due to
http://bugs.jquery.com/ticket/5445#comment:6 and the original code
using $.fn.position().

When edition buttons were moved to being children of the body (rather
than siblings of the image), $.fn.position() was replaced by
$.fn.offset() (to get the position of the image/link relative to the
body/page toplevel), the adjustment (addition of marginLeft/marginTop)
was left in, even though #5445 does not apply to $.fn.offset().

bzr revid: xmo@openerp.com-20140120144610-nu8q2naemzzhekv2

addons/website/static/src/js/website.editor.js

@@ -638,16 +638,14 @@
                 var $selected = $(this);
                 var position = $selected.offset();
                 if ($selected.is('img')) {
-                    var image_top = position.top + parseInt($selected.css('marginTop'), 10);
-                    var image_left = position.left + parseInt($selected.css('marginLeft'), 10);
                     $link_button.hide();
                     // center button on image
                     $image_button.show().offset({
                         top: $selected.outerHeight() / 2
-                                + image_top
+                                + position.top
                                 - $image_button.outerHeight() / 2,
                         left: $selected.outerWidth() / 2
-                                + image_left
+                                + position.left
                                 - $image_button.outerWidth() / 2,
                     });
                 } else {