upgraded django to 1.9.7 release

* Add Meta.fields = '__all__' to serializer classes where required.
* Add explicit on_delete=models.CASCADE to ForeignKey fields.
* Use '.remote_field' and '.model' in preference to '.rel' and '.to' when inspecting model fields.
* Use new value_from_object in preference to internal _get_val_from_obj

Update filtering.md

* updated guardians and filter versions
* Remove Django 1.10 from allow_failures

Do not list related field choices in OPTIONS requests.

Updated jquery version to 1.12.4

* Added TEMPLATES setting to tests
* Remove deprecated view-string in URL conf
* Replace 'urls = ...' in test classes with override_settings('ROOT_URLCONF=...')
* Refactor UsingURLPatterns to use override_settings(ROOT_URLCONF=...) style
* Get model managers and names in a version-compatible manner.
* Apply override_settings to a TestCase, not a mixin class
* Use '.callback' property instead of private attributes when inspecting urlpatterns
* Pass 'user' to template explicitly
* Correct sorting of import statements.
* Remove unused TEMPLATE_LOADERS setting, in favor of TEMPLATES.
* Remove code style issue
* BaseFilter test requires a concrete model
* Resolve tox.ini issues
* Resolve isort differences between local and tox environments

Clean up code style.

description.py codes and tests removal

Convert readthedocs link for their .org -> .io migration for hosted projects

As per [their blog post of the 27th April](https://blog.readthedocs.com/securing-subdomains/) ‘Securing subdomains’:

> Starting today, Read the Docs will start hosting projects from subdomains on the domain readthedocs.io, instead of on readthedocs.org. This change addresses some security concerns around site cookies while hosting user generated data on the same domain as our dashboard.

Test Plan: Manually visited all the links I’ve modified.

Wrap guardian.VERSION in tuple, in django-guardian 1.4.2 version has list type and comparison fails. (#4149)

* Use get_serializer_class in ordering filter* Test improper configuration of ordering* Raise ImproperlyConfigured when missing get_serializer_class

* Use get_serializer_class in ordering filter
* Test improper configuration of ordering
* Raise ImproperlyConfigured when missing get_serializer_class

Fix #3844, refine validator for fields with <source=> kwargs

When serializers has fields with something like `source=user.email`, the
uniqueness validator should check `email` field instead of `user`, cause
`user` is a model object.

* added django 1.10 alpha on tox
* added django 1.10 alpha on travis
* added allow_failure on travis matrix

`print` is available as a function on every supported version of Python (2.7+)

Drop out-of-date paragraph on `request.content`

Fix typos in ReturnDict and ReturnList docstrings