Check CSV files match the template

This commit adds a first stab at checking whether a CSV file has the right
data to fill the placeholders.

The UI is very much first bash, but I’d like to get this merged and see how it
feels. The main thing is that we’ve got all the bit in place now to do this
logic.

app/templates/views/send-sms.html

@@ -2,7 +2,7 @@
 {% from "components/sms-message.html" import sms_message %}
 {% from "components/page-footer.html" import page_footer %}
 {% from "components/file-upload.html" import file_upload %}
-{% from "components/table.html" import list_table %}
+{% from "components/table.html" import list_table, field %}
 
 {% block page_title %}
   Send text messages – GOV.UK Notify
@@ -16,7 +16,7 @@
 
     <div class="grid-row">
       <div class="column-two-thirds">
-        {{ sms_message(template.content) }}
+        {{ sms_message(template.formatted_as_markup) }}
       </div>
     </div>
 
@@ -35,13 +35,21 @@
 
     {% if column_headers %}
       {% call(item) list_table(
-        [],
+        example_data,
         caption='Preview',
         field_headings=column_headers,
         field_headings_visible=True,
         caption_visible=False,
         empty_message="Your data here"
       ) %}
+        {% call field() %}
+          {{ item.phone }}
+        {% endcall %}
+        {% for column in template.placeholders %}
+          {% call field() %}
+            {{ item.get(column) }}
+          {% endcall %}
+        {% endfor %}
       {% endcall %}
     {% endif %}
     <p class="table-show-more-link">