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/templates/views/check/row-errors.html

@@ -80,6 +80,12 @@
                   No content for this message
                 {% elif item.message_too_long %}
                   Message is too long
+                {% elif not item.as_postal_address.has_enough_lines %}
+                  Address must be at least {{ letter_min_address_lines }} lines long
+                {% elif item.as_postal_address.has_too_many_lines %}
+                  Address must be no more than {{ letter_max_address_lines }} lines long
+                {% elif not item.as_postal_address.postcode %}
+                  Last line of the address must be a real UK postcode
                 {% endif %}
               </span>
             {% endcall %}