Don’t show cancelled jobs anywhere

The information about a job doesn’t make sense if a job is cancelled.

We could change the information to reflect that the job won’t be sent/
wasn’t sent/was cancelled, but there’s nothing you can really do with
this info.

So instead let’s:
- hide cancelled jobs from the dashboard
- hide cancelled jobs from the jobs page
- 404 the page if the user tries to click back enough times to hit the
  job page

tests/conftest.py

@@ -872,6 +872,20 @@ def mock_get_scheduled_job(mocker, api_user_active):
     return mocker.patch('app.job_api_client.get_job', side_effect=_get_job)
 
 
+@pytest.fixture(scope='function')
+def mock_get_cancelled_job(mocker, api_user_active):
+    def _get_job(service_id, job_id):
+        return {"data": job_json(
+            service_id,
+            api_user_active,
+            job_id=job_id,
+            job_status='cancelled',
+            scheduled_for='2016-01-01T00:00:00.061258'
+        )}
+
+    return mocker.patch('app.job_api_client.get_job', side_effect=_get_job)
+
+
 @pytest.fixture(scope='function')
 def mock_get_job_in_progress(mocker, api_user_active):
     def _get_job(service_id, job_id):
@@ -903,7 +917,8 @@ def mock_get_jobs(mocker, api_user_active):
                 ("applicants.ods", '', ''),
                 ("thisisatest.csv", '', ''),
                 ("send_me_later.csv", '2016-01-01 11:09:00.061258', 'scheduled'),
-                ("even_later.csv", '2016-01-01 23:09:00.061258', 'scheduled')
+                ("even_later.csv", '2016-01-01 23:09:00.061258', 'scheduled'),
+                ("full_of_regret.csv", '2016-01-01 23:09:00.061258', 'cancelled')
             )
         ]}