Remove placeholder logs of notifications sent

From the:
- dashboard
- activity page

This info will be confusing for users at the hack day, because it will say
they’ve already sent messages when they first sign up.

This involved changing the table macro to have a nice ‘no rows’ message.

app/templates/views/styleguide.html

@@ -148,6 +148,21 @@
     {% endcall %}
   {% endcall %}
 
+  {% call(item) list_table(
+    [],
+    caption='Jobs',
+    field_headings=['Job', 'Time'],
+    caption_visible=True,
+    empty_message='You haven’t scheduled any jobs yet'
+  ) %}
+    {% call field() %}
+      {{ item.job }}
+    {% endcall %}
+    {% call field() %}
+      {{ item.time }}
+    {% endcall %}
+  {% endcall %}
+
   <h2 class="heading-large">Textbox</h2>
   {{ textbox(form.username) }}
   {{ textbox(form.password) }}