Merge branch 'fix_infinite_scroll_breaks_on_back_button_activity_feed' into 'master'

fix bug causing the infinite scrolling in activity feeds to break when you click a link and navigate back

![arrg_](/uploads/53b2a01d3b55938cc12c805e1a81ff6b/arrg_.gif)

See merge request !3835

app/views/projects/_activity.html.haml

@@ -9,4 +9,7 @@
 = spinner
 :javascript
-  new Activities();
+  var activity = new Activities();
+  $(document).on('page:restore', function (event) {
+    activity.reloadActivities()
+  })