polls url include must be before cms url include

In Step 3, we tell users to add the following line to their project's
urls.py:
python```
url(r'^polls/', include('polls.urls', namespace='polls')),
```
However, if they add it to the end, then django-cms will first modify the path
of the url from '/en/polls/' to '/en/polls/$'.
See https://github.com/divio/django-cms/blob/develop/cms/views.py#L40
This only manifests itself as an opaque 404, frustrating someone who is
following along with the tutorial and does not know why the newly-added
polls application fails to show up.
Merge pull request #30 from amfarrell/master

polls url include must be before cms url include