Fix processing of ManyToManyField when it is empty 

Signed-off-by: Fernando Rocha <fernandogrd@gmail.com>

Signed-off-by: Fernando Rocha <fernandogrd@gmail.com>

For ensuring `django-jsonfield` compatibility, via #629.

Update rest_framework/serializers.py

Ensure model field validation is performed for ModelSerializers with a custom restore_object method.  Fixes #623.

Login page styles fix. Closes #618. Made with 🍪

Fix small mistake in docs.

Added PATCH HTTP method to the docs

Conflicts:
	docs/api-guide/authentication.md

Update docs/tutorial/1-serialization.md

Update for tutorials (manual serialization) to support HTTP PATCH method (partial update of instance)

(Test also incoming)