Adding thumbnail image creation. Thumbnails will be utilized on the media tab

Adds migration for thumbnail image as well as overrides save
functionality for the media object so that we can create thumbnail on
save

Also excludes thumbnail from the TSMedia admin form
Updated due to feedback from @rlskoeser

Added logic to only generate thumbnail if the main image has changed or
if thumbnail doesn't exist yet. changed upload_to callbacks to use
os.path.splitext to handle filename extension splitting
Initial commit of media tab functionality

* Creates a two column grid of a tour stops media by utilizing the
jquery mobile grid functionality
* Created a tour_stop_media_detail view (maybe rename to
tour_media_detail because of url structure)
* Added media serving url to urls.py at root of project
* Setup media detail url to be <tour.slug>/<media.id>
* Created inline for tour stop admin, this is only viewable from the
individual tour admin, alternately you can create individula TSAdmins
in teh admin panel and manually assign the tour stop
Merge branch 'feature/media-display' into develop