Reset columns_selector before caching the page

This will allow to initialize this module again without duplicating
columns checkboxes and without breaking the page.

app/assets/javascripts/application.js

@@ -170,6 +170,7 @@ var initialize_modules = function() {
 var destroy_non_idempotent_modules = function() {
   "use strict";
 
+  App.ColumnsSelector.destroy();
   App.Datepicker.destroy();
   App.HTMLEditor.destroy();
   App.LegislationAnnotatable.destroy();

app/assets/javascripts/columns_selector.js

@@ -85,6 +85,9 @@
       $(".column-selectable").on("inserted", function() {
         App.ColumnsSelector.initColumns();
       });
+    },
+    destroy: function() {
+      $("#js-columns-selector-wrapper").children(":not(#column_selector_item_template)").remove();
     }
   };
 }).call(this);