Websites/Affiliates/AddingBanners/SpecialUpgrade

Original bug : https://bugzilla.mozilla.org/show_bug.cgi?id=719522

We need 3 images per banner: the upgrade version, a neutral version and a split version for the preview.

Steps to upload a new version of a banner (new color, locale, size)

1. Send the "split" and "upgrade" version of the banner to a dev.
2. Dev: Get the hash for the new images
   hashlib.sha1("%id_%width_%height_%color_%locale").hexdigest()
3. Dev: Updates apps/banners/management/commands/banners_htaccess.py to include this hash
4. Dev: In the media/static_banners directory, adds {hash}.from_affiliates.[png|jpg] and {hash}.upgrade.[png|jpg]
5. Dev: git commit, deploy (this will run the banners_htaccess command)
6. You can now upload the neutral version and everything should work.