Add postal address row errors

Context:
- postal addresses can be made from any of the 7 address lines now, and
  the postcode can be in any one of the 7
- we can put errors across a whole row now, not just on individual cells

This commit put errors to do with the postal address as a whole across
the whole row now, rather than tying them to any one cell.

app/main/views/send.py

@@ -711,6 +711,8 @@ def _check_messages(service_id, template_id, upload_id, preview_row, letters_as_
         ),
         letter_too_long=is_letter_too_long(page_count),
         letter_max_pages=LETTER_MAX_PAGE_COUNT,
+        letter_min_address_lines=PostalAddress.MIN_LINES,
+        letter_max_address_lines=PostalAddress.MAX_LINES,
         page_count=page_count
     )