js: insert maps once the page is fully loaded (#6609)

This makes sure the correct element height is known, and that avoids an
half-gray zone in Chrome.

wcs/qommon/static/js/qommon.map.js

@@ -1,4 +1,4 @@
-$(function() {
+$(window).on('load', function() {
   $('.qommon-map').each(function() {
      var $map_widget = $(this);
      var map_options = Object();