Initialize only visible maps when page is loaded

Its known that initializing a map when it is inside a hidden element
wont work when hidden element is shown, so its makes sense to
avoid initialization of hidden maps.

When a map lives within a hidden layer we need to initialize the
map after the event of showing that hidden layer, in our case when
admin settings tab is shown.

app/assets/javascripts/map.js

@@ -2,7 +2,7 @@
   "use strict";
   App.Map = {
     initialize: function() {
-      $("*[data-map]").each(function() {
+      $("*[data-map]:visible").each(function() {
         App.Map.initializeMap(this);
       });
       $(".js-toggle-map").on({