Adds missing migration for Django 1.7

Working to test django-cms 3.0.5 against Django 1.7, and came across some missing migrations.  Found a couple others in the djangocms-inherit and djangocms-link repos and submitted PRs ([1](https://github.com/divio/djangocms-link/pull/22), [2](https://github.com/divio/djangocms-inherit/pull/6)) there also.

I'm going to deploy this to Heroku and play around a bit.  I'll let you know if any issues come up.  I've looked around for a milestone / roadmap to 1.7 final support, but couldn't get a good sense of status other than a few open issues referencing 1.7.  If you have a second, can you give me a brief update on where that stands, or better yet, point me to any documentation I may have overlooked.  Thanks!