Allow use of native migrations in 1.7 — Take 2

Conflicts:
	rest_framework/fields.py

Update fields.md

obj.__class__ will return the actual Class object, we want to serialise a string (accessed with obj.__class__.__name__)

Modelserialization charfield with null

Fixes #1651. Add link to drf-extensions nested routers to docs

Conflicts:
	docs/topics/release-notes.md

Added (first pass) notes to docs & release notes. Backed out `SOUTH_MIGRATION_MODULES` setting from `rest_framework.settings`

Conflicts:
	.travis.yml
	docs/api-guide/viewsets.md
	rest_framework/serializers.py
	rest_framework/throttling.py
	tests/test_generics.py
	tests/test_serializers.py
	tox.ini

tiny typo in the docstring

Version 2.3.14

Fix #1614 - Corrected reference to serializers.CharField