Use score summaries in data download

The submissions API has a get_score() method which, given a student item,
will look up the relevant ScoreSummary and return the latest Score it
contains. Our data download should do the same.

To avoid confusion, we have elected to hide scores that could not be
returned from api.get_score(). The other options are:
- include a score that may be for a different submission for the same
    student item, if using ScoreSummary.latest in all cases
- include scores that may not "count", because they'll never be the
    return value of api.get_score()

Test has been updated.

Update versioning to 1.0.0

Sibling to https://github.com/edx/edx-ora2/pull/886.
edx-submissions is rather stable, and should be bumped to a 1.0.0 release

Use the docker infrastructure for travis builds.

Add pep8 and pylint linting updates.

Version 0.1.4

Soft-delete Submissions to reset student state

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.