Change display of placeholder columns

On the send page, it should hightlight the placeholders so they match
what you need to put in the CSV file.

On the check page, they should not be highlighted, to match what’s in
the (rendered) template.

app/templates/views/send.html

@@ -43,7 +43,7 @@
     example,
     caption="Example",
     caption_visible=False,
-    field_headings=['1'] + [recipient_column] + template.placeholders|list
+    field_headings=['1'] + [recipient_column] + template.placeholders_as_markup|list
   ) %}
     {{ index_field(row_number) }}
     {% for column in item %}