Add two-way messaging view

> Once an inbound message has been received, there should be a way to
> see the other messages in the system from the same service to the same
> number. Both in and outbound. Nice inbox/whatsapp stylee view or some
> such. This way the context of the reply is understood.
>
> Initially will only see the outbound template, not the actual message,
> but we’re going to change this for the rest (soon), so that you can
> always see the full message for all outbound.

app/templates/views/conversations/conversation.html

@@ -0,0 +1,50 @@
+{% extends "withnav_template.html" %}
+
+{% block service_page_title %}
+  Conversation
+{% endblock %}
+
+{% block maincolumn_content %}
+
+  <div class="dashboard">
+
+    <div class="bottom-gutter">
+      <h1 class="heading-large">
+        07900 900 123
+      </h1>
+    </div>
+    {% for message in conversation %}
+      <div class="grid-row" id="n{{ message.id }}">
+        {% if message.inbound %}
+          <div class="column-two-thirds sms-message-inbound">
+            {{ message.content | string }}
+            <div class="sms-message-status">
+              {{ message.created_at | format_datetime_relative }}
+            </div>
+          </div>
+        {% else %}
+          <div class="column-one-third">
+            &nbsp;
+          </div>
+          <div class="column-two-thirds">
+            {{ message.content | string }}
+            {% if message.status == 'delivered' %}
+              <div class="sms-message-status sms-message-status-outbound">
+                {{ message.created_at | format_datetime_relative }}
+              </div>
+            {% elif message.status in ['pending', 'sending', 'created'] %}
+              <div class="sms-message-status sms-message-status-outbound hint">
+                sending
+              </div>
+            {% else %}
+              <div class="sms-message-status sms-message-status-outbound table-field-error-label">
+                Failed (sent {{ message.created_at | format_datetime_relative }})
+              </div>
+            {% endif %}
+          </div>
+        {% endif %}
+      </div>
+    {% endfor %}
+  </div>
+
+{% endblock %}