Added command to run a bash shell in the docker dev environment

I'm running a bunch of these to debug the image upload error and it's
nice to have something that cleans up after you're done.
Fix thumbnail uploads (#920)

The uploads were failing because we used a really old version of
sorl-thumbnail.  Replaced that with code that uses easy_thumbnails to
create the thumbnails.  Also replaced PIL with a recent version of
Pillow.

Removed the thumb_options parameter.  We weren't really using it.  Now
we always upscale and use crop=smart (which was the default before).
Merge branch 'gh-997' into gh-920
Removed the thumb_options paramater from S3EnabledImageField.

We aren't honoring that parameter anymore, so I removed it from the
options.

Added a bunch of empty migrations so that south updates it's tables
with the new spec for the field.
Fixed the amara-dev Dockerfile.

The ln -s command complained that the file was missing.  I guess we
don't need to do this anymore now that we're using Pillow.

Removed sorl.thumbnail from the INSTALLED_APPS setting.
Removed references to the sorl-thumbnail's template tags
Merge pull request #1003 from pculture/gh-920

Gh 920