Remove the ‘manage templates’ page

The ‘manage templates’ page was almost identical to the ‘send text messages’
page.

This commit consolidates them into one and makes them all hang together.

Part of this means tweaks to the javascript so that files upload as soon as
you’ve chosen them.

app/templates/views/send-sms.html

@@ -20,16 +20,11 @@
       </div>
     </div>
 
-    {{file_upload(form.file, button_text='Choose a CSV file')}}
-
     <p>
       <a href="{{ url_for('.get_example_csv', service_id=service_id, template_id=template.id) }}">Download an example CSV file</a>
     </p>
 
-    {{ page_footer(
-      "Continue to preview"
-    ) }}
-
+    {{file_upload(form.file, button_text='Upload a CSV file')}}
 
   </form>
 {% endblock %}