Add context to exception handler #2236

Same context as renderers which include: the view,
args, kwargs, and request.

This provides enough contextual information to the
exception handlers to handle errors better.

In a use case like #1671, a custom handler
would allow Sentry to log the request properly.
Support handlers with and without context
Remove test
Update docs
Add pending deprecation warning message
Reuse exception_handler variable throughout
Add get_exception_handler_context()
Update excepteion_handler signature
First pass at serializer repr bug
Merge branch 'exception-handler-context' of git://github.com/jpadilla/django-rest-framework into jpadilla-exception-handler-context
Merge branch 'exception-handler-context' of git://github.com/jpadilla/django-rest-framework into version-3.1
Merge branch 'jpadilla-exception-handler-context' into version-3.1