Make example on send look more like a spreadsheet

Now that the example on the breaking changes page looks more like a spreadsheet,
we should do the same thing for the downloadable example on the send page.

app/main/views/send.py

@@ -1,5 +1,7 @@
 import json
 import itertools
+from string import ascii_uppercase
+
 from contextlib import suppress
 from zipfile import BadZipFile
 from xlrd.biffh import XLRDError
@@ -127,8 +129,11 @@ def send_messages(service_id, template_id):
     return render_template(
         'views/send.html',
         template=template,
-        recipient_column=first_column_heading[template.template_type],
-        example=[get_example_csv_rows(template)],
+        column_headings=list(ascii_uppercase[:len(template.placeholders) + 1]),
+        example=[
+            [first_column_heading[template.template_type]] + list(template.placeholders),
+            get_example_csv_rows(template)
+        ],
         form=form
     )
 

app/main/views/templates.py

@@ -1,4 +1,4 @@
-import string
+from string import ascii_uppercase
 
 from flask import request, render_template, redirect, url_for, flash, abort, session
 from flask_login import login_required
@@ -127,7 +127,7 @@ def edit_service_template(service_id, template_id):
                 'views/templates/breaking-change.html',
                 template_change=template_change,
                 new_template=new_template,
-                column_headings=list(string.ascii_uppercase[:len(new_template.placeholders) + 1]),
+                column_headings=list(ascii_uppercase[:len(new_template.placeholders) + 1]),
                 example_rows=[
                     [first_column_heading[new_template.template_type]] + list(new_template.placeholders),
                     get_example_csv_rows(new_template),