Updates ownership views to support S3 deliveries

[dleehr]

• Rewrites ownership/views.py to use class-based views
• Delivery acceptance/rejection/details classes are plugged in via a DeliveryType class
• Adds a transfer_id field to S3Delivery, as an auto-generated UUID
• Moves decline_delivery into DeliveryUtil
• Updates HTML templates to be compatible with S3 as well
• Adds a delivery_type field to HTML forms and query strings. Can be dds or s3. If missing, will default to dds

Fixes #131

[dleehr]

I have not tested that the email templates use the transfer_id as expected - emailing was out of scope for this feature so I've been constructing the URLs manually

Summary of my testing on local dev environment:

1. Create 3 django users: sender, receiver, agent
2. Create S3UserCredentials for each. Since I had two credentials, I used one for sender and agent and the other for receiver
3. As the sender:

   s3 mb s3://d4s2-test-2018-04-25
   s3 cp d4s2-test-2018-04-25/hello.txt s3://d4s2-test-2018-04-25
   datadelivery deliver -b d4s2-test-2018-04-25 --email receiver-email@domain.com

4. Confirm S3Delivery created in API and email printed out to console
5. Get the transfer_id from the S3 delivery:

   python manage.py shell
   >>> from d4s2_api.models import S3Delivery
   >>> str(S3Delivery.objects.first().transfer_id)
   '0c328d98-b40a-4e12-ba3b-64076db6b7f5'

6. As the receiver, login to D4S2 using django credentials
7. Construct url with delivery_type and transfer_id http://localhost:8000/ownership/?delivery_type=s3&transfer_id=0c328d98-b40a-4e12-ba3b-64076db6b7f5
8. Accept the delivery
9. Confirm that the sender can no longer see a project, but the receiver has a copy.

[johnbradley]

I'm still reviewing this, accidentally click the wrong option.

[dleehr]

@johnbradley: 07875ccfb872f912e7e3f33072f2d79f57da8000 adds consistent checking for completed deliveries in the areas you caught.