* fix type mismatch in course_goals migrations
* fix type mismatch in experiments migrations
* fix type mismatch in xblock_django migrations
* fix type mismatch in catalog migrations
* fix type mismatch in static_replace migrations
* fix type mismatch in bulk_email migrations
* fix type mismatch in course_overviews migrations
To be able to more easily deal with same-origin issues, due to some course assets being loaded in an iframe, we're adding the ability to specify file extensions that should be excluded from URL canonicalization. The default value is simply 'html', which means we won't rewrite asset links that point to files ending in .html. Thus, they'll be loaded from the same origin as the parent page, and voila, no SOP issues.
