Add tag filter to debates page

app/assets/javascripts/application.js

@@ -33,6 +33,7 @@ var initialize_modules = function() {
   App.Stats.initialize();
   App.LocaleSwitcher.initialize();
   App.DebatesOrderSelector.initialize();
+  App.DebatesTagFilter.initialize();
 };
 
 $(function(){

app/assets/javascripts/debates_tag_filter.js.coffee

@@ -0,0 +1,17 @@
+App.DebatesTagFilter =
+
+  href_with_params: (query_params) ->
+    loc = window.location
+
+    loc.protocol + "//" + loc.hostname +
+      (if loc.port then ':' + loc.port else '') +
+      loc.pathname +
+      loc.hash +
+      '?' + $.param(query_params)
+
+  initialize: ->
+    $('.js-tag-filter').on 'change', ->
+      query_params = window.getQueryParameters()
+      query_params['tag'] = $(this).val()
+      window.location.assign(App.DebatesTagFilter.href_with_params(query_params))
+