Previous methods of "deleting state" for a student had just issued
reset scores, so the (unscored) submission was still hanging around.
With this change, the submission can be "deleted" for all django-
relevant purposes, while still remaining in the database in case
it turns out to be interesting to analytics later.

Includes a migration that may take some time to run, and will acquire a
table lock. This will cause an outage for any other request trying to
hit the submissions table during the migration. We've estimated the outage
to last approximately 3 minutes on a database with 700,000 rows.

Test also included.

Update the DRF version requirement to match edx-platform

Add new app_label to ScoreAnnotation.

Django upgrade/1.8 release

Conflicts:
	setup.py
	submissions/models.py

We had made the migrations from master, but that isn't what edx-platform
was using yet.  This migration is re-made from 0.1.0, which removes
things that happened after 0.1.0.

remove deprecation warnings

Update the submission version.

Add the ability to annotate scores.

Upgrade djangorestframework to v3.1

update django-nose

* Upgrade DRF to v3.1
* Use JSONField on the model instead of custom serializer field for the submission answer.

Upgrade django-model-utils to 2.3.1

Update pytz to reflect upstream version change

In certain circumstances the version of Pytz in this file will conflict with versions of pytz required by edx-platform in `requirements/edx/base.txt`. This PR makes the version in this repository match.

Upgrade django-extensions to 1.5.5

Add get_all_submissions method to the API

This is consistent with the default ordering of the model and avoids ties in
case to items have the same timestamp.

Adding signals for scoring events.

The Top submissions should not be including the cancelled ones.

TNL-1455