Add row numbers to tables

When a table is showing the contents of a CSV file, it should look
something like a spreadsheet.

The minimally skeuomorphic way to do this is by adding row numbers.

This commit doesn’t
- make the row numbers monospace (it’s barely noticeable and doesn’t
  reflect what actual spreadsheets do)
- make the first column heading ‘Row’ (again, doesn’t reflect how actual
  spreadsheets work, and takes up more valuable space)

app/templates/views/user-profile.html

@@ -9,7 +9,7 @@
 
   <h1 class="heading-large">Your profile</h1>
 
-  {% call(item) list_table(
+  {% call(item, row_number) list_table(
     [
       {'label': 'Name', 'value': current_user.name, 'url': url_for('.user_profile_name')},
       {'label': 'Email address', 'value': current_user.email_address, 'url': url_for('.user_profile_email')},