update tutorial for Django 1.7 (and django CMS 3.1)

[stefanfoulis]

• pull request for updated polls app: Django 1.7 compatibility divio/django-polls#2
• code of the tutorial, one commit per step: https://github.com/divio/djangocms-tutorial-code/commits/master

[coveralls]

Coverage remained the same at 90.78% when pulling 603bc20 on stefanfoulis:feature/tutorial-django-1.7-compat into 5af5648 on divio:develop.

[coveralls]

Coverage remained the same at 90.78% when pulling 603bc20 on stefanfoulis:feature/tutorial-django-1.7-compat into 5af5648 on divio:develop.

[stefanfoulis]

@yakky @mkoistinen please review. Would be awesome if we could merge this into develop before the Tutorial at djangocon.eu (Sunday 31. May 13:00 GMT)

(/cc @evildmp )

[coveralls]

Coverage remained the same at 90.78% when pulling 63cf4d0 on stefanfoulis:feature/tutorial-django-1.7-compat into 5af5648 on divio:develop.

[coveralls]

Coverage remained the same at 90.78% when pulling 63cf4d0 on stefanfoulis:feature/tutorial-django-1.7-compat into 5af5648 on divio:develop.

[coveralls]

Coverage remained the same at 90.78% when pulling 63cf4d0 on stefanfoulis:feature/tutorial-django-1.7-compat into 5af5648 on divio:develop.

[coveralls]

Coverage remained the same at 90.78% when pulling 3c7c44f on stefanfoulis:feature/tutorial-django-1.7-compat into 5af5648 on divio:develop.

[coveralls]

Coverage remained the same at 90.78% when pulling 3c7c44f on stefanfoulis:feature/tutorial-django-1.7-compat into 5af5648 on divio:develop.

[coveralls]

Coverage remained the same at 90.78% when pulling 3c7c44f on stefanfoulis:feature/tutorial-django-1.7-compat into 5af5648 on divio:develop.