Create media objects from base64 data in Summernote throughout the site

Wrote a migration per the suggestion of @jdalphon during our meeting this week.  The migration will save any Projects, Users, Tutorials, News articles, and Visualizations currently on the site.  Since the creation of media objects from summernote occurs as the result of a before_save callback, simply saving the records in the database will suffice to remove all base64 image data from the site, and replace it with saved media objects.