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/_jobs.html

@@ -26,22 +26,22 @@
         {% endif %}
         <span class="file-list-hint">
           Sent {{
-            (item.scheduled_for if item.scheduled_for else item.created_at)|format_datetime_relative
+            (item.scheduled_for or item.created_at)|format_datetime_relative
           }}
         </span>
       </div>
     {% endcall %}
     {% call field() %}
       {{ big_number(
-        item.get('notification_count', 0) - item.get('notifications_delivered', 0) - item.get('notifications_failed', 0),
+        item.notifications_sending,
         smallest=True
       ) }}
     {% endcall %}
     {% call field() %}
-      {{ big_number(item.get('notifications_delivered', 0), smallest=True) }}
+      {{ big_number(item.notifications_delivered, smallest=True) }}
     {% endcall %}
-    {% call field(status='error' if item.get('failure_rate', 0) > 3 else '') %}
-      {{ big_number(item.get('notifications_failed', 0), smallest=True) }}
+    {% call field(status='error' if item.high_failure_rate else '') %}
+      {{ big_number(item.notifications_failed, smallest=True) }}
     {% endcall %}
   {% endcall %}
 </div>

app/templates/views/dashboard/_upcoming.html

@@ -3,7 +3,7 @@
 {% from "components/show-more.html" import show_more %}
 
 <div class="ajax-block-container">
-  {% if scheduled_jobs %}
+  {% if current_service.scheduled_jobs %}
     <div class='dashboard-table'>
       {% if not hide_heading %}
         <h2 class="heading-medium heading-upcoming-jobs">
@@ -11,7 +11,7 @@
         </h2>
       {% endif %}
       {% call(item, row_number) list_table(
-        scheduled_jobs,
+        current_service.scheduled_jobs,
         caption="In the next few days",
         caption_visible=False,
         empty_message='Nothing to see here',

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),