fix contact list bst bug

the api returns UTC timestamps, we should keep them as UTC timestamps
until the very last moment, and only convert them into BST when we know
we want to return to a user (ie: in contact-list.html and other places
like that)

tests/app/models/test_contact_list.py

@@ -1,15 +1,7 @@
-from datetime import datetime
-
 from app.models.contact_list import ContactList
 from app.models.job import PaginatedJobs
 
 
-def test_created_at():
-    created_at = ContactList({'created_at': '2016-05-06T07:08:09.061258'}).created_at
-    assert isinstance(created_at, datetime)
-    assert created_at.isoformat() == '2016-05-06T08:08:09.061258+01:00'
-
-
 def test_get_jobs(mock_get_jobs):
     contact_list = ContactList({'id': 'a', 'service_id': 'b'})
     assert isinstance(contact_list.get_jobs(page=123), PaginatedJobs)