Use a ModelList for lists of jobs

This follows the pattern of what we’ve done with services, users and
events.

It gives us a way of neatly instantiating a model for each item in the
list we get back from the API and reduces the complexity of the view
layer code.

Now is a good time to do this because we’re going to be making a bunch
of changes to the jobs pages, and those changes will be easier to code
and understand with a sensible model behind them.

tests/app/main/views/test_dashboard.py

@@ -1366,7 +1366,8 @@ def test_should_show_all_jobs_with_valid_statuses(
     mock_get_service_templates_when_no_templates_exist,
     mock_get_jobs,
     mock_get_usage,
-    mock_get_inbound_sms_summary
+    mock_get_inbound_sms_summary,
+    mock_get_free_sms_fragment_limit,
 ):
     logged_in_client.get(url_for('main.service_dashboard', service_id=SERVICE_ONE_ID))