[FIX] don't close editor dialogs on click *around* the dialog

APR double-clicks images in the image sub-popup (browse existing), if
an image on a side (outside the initial dialog's rect) is picked the
first click will select it and close the dialog, and the second one
will land on the base dialog's backdrop, cancelling & closing it.

bzr revid: xmo@openerp.com-20131014100944-3xtbiyj063fmzhko

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

@@ -483,7 +483,7 @@
         },
         start: function () {
             var sup = this._super();
-            this.$el.modal();
+            this.$el.modal({backdrop: 'static'});
             return sup;
         },
         save: function () {