Handle multi-column recipients

Implements https://github.com/alphagov/notifications-utils/pull/81

Handles addresses as multiple columns:
- in ‘Send yourself a test’
- in example CSV files
- in validating that a CSV file has recipients (eg at least an ‘address
  line 1’ and ‘postcode’ column)
- when showing the contents of a CSV file

As few UI changes as possible, once we have the thing working end-to-end
we can think about how the UI might need to work differently.

app/templates/views/check.html

@@ -31,7 +31,7 @@
       {% endcall %}
     </div>
 
-  {% elif not recipients.has_recipient_column %}
+  {% elif not recipients.has_recipient_columns %}
 
     <div class="bottom-gutter">
       {% call banner_wrapper(type='dangerous') %}
@@ -193,7 +193,9 @@
           {{ item['columns'][column].data if item['columns'][column].data != None }}
         {% endcall %}
       {% else %}
-        {{ text_field(item['columns'][column].data) }}
+        {% call field() %}
+          {{ item['columns'][column].data if item['columns'][column].data != None }}
+        {% endcall %}
       {% endif %}
     {% endfor %}
     {% if item['columns'].get(None) %}