The JSON returned by FoldersController#index includes the special "all" folder, which is the
folder that will contain all subscribed feeds in the sidebar.
Feeds are retrieved in a JSON list via AJAX, and used with angularjs to render the sidebar.

Complex json views are used for FeedsController#index and FoldersController#index because the values returned in the JSON are not a simple JSON serialization of a model instance:

- in the case of folders, a special "all" folder is returned which doesn't actually exist in the database
- in the case of feeds, some of the fields returned are not present in the feed model but are retrieved from other models or method calls.