Integrate OSF with Mailchimp

Add script to subscribe all registered
osf users to the general OSF mailing
list on mailchimp. Also add new users
to the list when they have registered and
confirmed their email address.
Add tests for OSF MailChimp functions

Test get_list_id_from_name() and subscribe()
functions. Also add tests for sync_email
script.
Add mailchimp to requirements.txt
Fix failing tests
Refactor mailchimp code into separate settings page

- Add notifications page under user settings and
  link in settings navigation side bar
- Add separate GET and POST routes to update
  subscribe info on the user
- Change user field to a dict ('mailing_lists')
  to support multiple lists.
  Format: {'list_name': True/False}
- Add unsubscribe helper to framework/auth/utils.py
Handle errors when user is already subscribed/unsubscribed
Change webhook url to api endpoint

- Add secret key as a parameter to
verify that mailchimp is posting
data to the url.
- Add GET endpoint for mailchimp
to hit (previously mailchimp did
not recognize the url given for
the webhook because it would return
a 404)
Test added view functions and mailchimp utils

Includes:
- mailchimp unsubscribe util
- mailchimp get list id from name util
- webhook routes
- route for updating lists on the user
Add tests for view, update, and delete
Add back datetime, remove unnecessary kwarg
Fix typo in comment
Add function to set expiration time (24 hours) for email token
Modify tests to account for expiration of email tokens
Primary change: set up an expired token for a user in test_verify_confirmation_token,
confirmed that it returned false.

Several other functions had to be modified, because the email_verifications[token]
dict now has 2 elements, not 1.
Update comment to reflect changed dict object for email_verifications
Merge branch 'develop' of github.com:CenterForOpenScience/osf.io into feature/expire-email-token
Fix a flake8 error, remove assignment to variable
Fix an off by one error
Merge branch 'develop' of github.com:CenterForOpenScience/osf.io into feature/github-crud-test-stubs
Merge branch 'develop' of https://github.com/CenterForOpenScience/osf.io into feature/mailchimp

Conflicts:
	framework/auth/views.py
Change `import celery` to `import app`