blessings for shell_plus

[bbearce]

@ mention of reviewers

@Didayolo

A brief description of the purpose of the changes contained in this PR.

We perform this sequence to get shell access to the django container:

docker-compose exec django bash
python manage.py shell_plus --plain # We only do this because blessings was missing

Now we can use shell_plus:

docker-compose exec django bash
python manage.py shell_plus

Issues this PR resolves

• add blessings to requirements.txt #1150

A checklist for hand testing

• run docker-compose exec django bash; python manage.py shell_plus to test
• check docs are the way we want them (change docs post accepting PR)

From the docs...:

With superuser privileges, the user can edit any benchmark and can access the Django admin interface.
from

docker-compose exec django bash
python manage.py shell_plus --plain
>>> u = User.objects.get(username=<USERNAME>) # can also use email
>>> u.is_staff = True
>>> u.is_superuser = True
>>> u.save()

to:

docker-compose exec django bash
python manage.py shell_plus
>>> u = User.objects.get(username=<USERNAME>) # can also use email
>>> u.is_staff = True
>>> u.is_superuser = True
>>> u.save()

Checklist

• Code review by me
• Hand tested by me
• I'm proud of my work
• Code review by reviewer
• Hand tested by reviewer
• CircleCi tests are passing
• Ready to merge