input letter address data in a single block

rather than in multiple placeholders - this is the first step towards
making postcodes non-required, which is the first step towards
international letters.

they still populate address_line_# and postcode fields under the hood -
to keep validation working the same, the last line always goes into
`postcode`.

the form normalises whitespace, removes extra new lines, and enforces
that you have between three and seven lines.

if the letter repeats address placeholders further down (eg "Dear
((address_line_1))"), then it'll fill those in as well. It'll still
prompt you to fill them in, but they'll be pre-filled.

app/templates/views/send-one-off-letter-address.html

@@ -0,0 +1,45 @@
+{% extends "withnav_template.html" %}
+{% from "components/page-header.html" import page_header %}
+{% from "components/page-footer.html" import page_footer %}
+{% from "components/message-count-label.html" import recipient_count_label %}
+{% from "components/textbox.html" import textbox %}
+{% from "components/form.html" import form_wrapper %}
+
+{% block service_page_title %}
+  {{ page_title }}
+{% endblock %}
+
+{% block maincolumn_content %}
+
+  {{ page_header(
+    page_title,
+    back_link=back_link
+  ) }}
+
+  {% call form_wrapper(
+    class='send-one-off-form',
+    module="autofocus",
+    data_kwargs={'force-focus': True}
+  ) %}
+    <div class="govuk-grid-row">
+      <div class="govuk-grid-column-two-thirds {% if form.placeholder_value.label.text == 'phone number' %}extra-tracking{% endif %}">
+        {{ textbox(
+          form.address,
+          rows=4,
+          width='1-1',
+          autofocus=True,
+          autosize=True,
+        ) }}
+      </div>
+    </div>
+    <p>
+      <a class="govuk-link govuk-link--no-visited-state" href="{{ url_for('.send_messages', service_id=current_service.id, template_id=template.id) }}">
+        Upload a list of {{ recipient_count_label(999, template.template_type) }}
+      </a>
+    </p>
+    {{ page_footer('Continue') }}
+  {% endcall %}
+
+  {{ template|string }}
+
+{% endblock %}

app/templates/views/templates/_template.html

@@ -16,11 +16,11 @@
     <div class="bottom-gutter-2-3">
       <div class="govuk-grid-row">
         {% if template.template_type == 'letter' %}
-        {% if letter_too_long %}
-          {% call banner_wrapper(type='dangerous') %}
-              {% include "partials/check/letter-too-long.html" %}
-          {% endcall %}
-        {% endif %}
+          {% if letter_too_long %}
+            {% call banner_wrapper(type='dangerous') %}
+                {% include "partials/check/letter-too-long.html" %}
+            {% endcall %}
+          {% endif %}
           {% if current_user.has_permissions('send_messages', restrict_admin_usage=True) and not letter_too_long %}
             <div class="govuk-grid-column-one-half">
               <a href="{{ url_for(".set_sender", service_id=current_service.id, template_id=template.id) }}" class="govuk-link govuk-link--no-visited-state pill-separate-item">