Use community conventions for model structure.
Add transitively_similar_movies property.
Use transitively_similar_movies property in admin.
Fix typo in secrets_template.py.
Add secrets.py to flake8 exclude list.
Move Amazon API logic into model.

This commit implements new attributes and a custom model manager
that allow us to handle associating data from the Amazon Product
Advertising API with movie objects in QuerySets instead of in
view logic.
Add unit test for Amazon model attribute default values.
Replace assertEqual None with assertIsNone.
Add unit test for model attributes whe Amazon API is unavailable.
Follow a convention in structure of models file contents.
Add unit test for the transitively_similar_movies property.
Use clearer naming in tests.
Use cleaner syntax when generating test objects.
Stick to a convention for indentation on multiline declarations.
Merge branch 'move_amazon_to_model'

This moves the code that handles the Amazon Product Advertising
API from view into model. It also sneaks in some cleaning of the
model code and tests.