Make target filter change when goal filter changes

Note we're using both the `hidden` and `disabled` properties to
guarantee compatibility with user agents which might still display the
option even when using the `hidden` attribute or hiding it with
`display: none`. We could also use `hide()` and `show()` instead of the
`hidden` property, but since we're using the `disabled` property, I
thought the code would be easier to read if we used properties in both
cases.

Also note users will no longer be able to get, let's say, debates which
are related to goal 1 and target 2.1. We think this use case is highly
unlikely and there's no need to take it into account.

app/assets/javascripts/application.js

@@ -112,7 +112,8 @@
 //= require columns_selector
 //= require budget_edit_associations
 //= require datepicker
-//= require sdg/related_list_selector
+//= require_tree ./sdg
+//= require_tree ./sdg_management
 
 var initialize_modules = function() {
   "use strict";
@@ -166,6 +167,7 @@ var initialize_modules = function() {
   App.BudgetEditAssociations.initialize();
   App.Datepicker.initialize();
   App.SDGRelatedListSelector.initialize();
+  App.SDGManagementRelationSearch.initialize();
 };
 
 var destroy_non_idempotent_modules = function() {