Allow encoding of an activity with configuration preset durations

fix #11

The activity form allow to receive pre-configured activity durations.

Those duration can be configured through the option
chill_activity.form.time_duration :

```yaml

chill_activity:
   form:
      time_duration:
         - { label: '12 minutes', seconds: 720 }
         # - ...

```

If a pre-existing activity receives a different time, the time is added
to the list of pre-configured duration time.

Controller/ActivityController.php

@@ -289,7 +289,7 @@ class ActivityController extends Controller
                     $this->get('translator')
                         ->trans('Success : activity updated!')
                 );
-
+//die();
             return $this->redirect($this->generateUrl('chill_activity_activity_show', array('id' => $id, 'person_id' => $person_id)));
         }