Calls to items() and values() return an iterator in Python 3. This
commit converts the result to a list if necessary. In some instances,
using the six helpers was not necessary and has been removed.

See also:
https://docs.djangoproject.com/en/dev/topics/python3/#dict-and-dict-like-classes

The function essentially does two things:
1. it applies a prefix - the first argument - to the given urls. In no
   instance a prefix was given
2. it calls url() for simple tuple or list elements in the given iterable.
   Cases where such a tuple or list was passed to patterns have been
   replaced by direct calls to url()

2 allowed for both calls to url() and simple tuples to be listed in
get_urls() and similar places. This allowed for unnecessary variation.
Always calling url() makes the url lists look less noisy and more uniform,
allowing the reader to focus on the actual differences of the urls instead
of superfluities.

django.conf.urls.patterns will also undergo deprecation starting from
Django 1.8. This commit anticipates that change.

https://docs.djangoproject.com/en/dev/releases/1.8/#django-conf-urls-patterns

Now using Napoleon :)

- Expand the ref/apps docs. (Still lots to do here.)
- Split up the index page links for clarity.

Fixes #967

Allows specifying default permissions and individual permissions based
on view names.

Introduces the concept of a "feature" that can be hidden. A list of
features to hide can be supplied in OSCAR_HIDDEN_FEATURES.

Feature hiding is currently supported in two places.
Application instances can carry a "hidable_feature_name". If set and
found in OSCAR_HIDDEN_FEATURES, post_process_urls will return an empty
set of url patterns, hence disabling relevant views.
display_tags also has a new template block tag iffeature.
{% iffeature "feature" %}xxx{% endiffeature %} will hide everything
inside the block if the feature is hidden.

This uses a few new methods in oscar.core.application.Application which
enable custom decorators to be set for given view fns.

The main use case at the moment is to make it easy to ensure that
checkout is not available to non-logged-in users when
OSCAR_ALLOW_ANON_CHECKOUT is set to False.

tests