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.

app/templates/views/dashboard/dashboard.html

@@ -35,7 +35,7 @@
 
     {{ ajax_block(partials, updates_url, 'template-statistics', interval=5) }}
 
-    {% if partials['has_jobs'] %}
+    {% if current_service.immediate_jobs %}
       {{ ajax_block(partials, updates_url, 'jobs', interval=5) }}
       {{ show_more(
         url_for('.view_jobs', service_id=current_service.id),