Show upcoming jobs on the dashboard

On the dashboard:
- adds a new ‘in the next 24 hours’ section to the dashboard which lists
  upcoming jobs
- tweaks some spacing on the dashboard so that it doesn’t look like too
  much of a mess
- don’t show scheduled jobs in the table of normal jobs

On the jobs page:
- don’t show scheduled jobs

app/templates/components/show-more.html

@@ -1,3 +1,7 @@
-{% macro show_more(url, label) %}
-  <a href="{{ url }}" class="show-more"><span>{{ label }}</span></a>
+{% macro show_more(url=None, label=None) %}
+  {% if url and label %}
+    <a href="{{ url }}" class="show-more"><span>{{ label }}</span></a>
+  {% else %}
+    <span class="show-more-empty"></span>
+  {% endif %}
 {% endmacro %}