Put message previews on ‘Send SMS’ page

A previous commit removed these to differentiate between this page and the
manage templates page. It turns out that we do want previews on this page
because:
- the users for the two pages might be different—they might only be allowed to
  do one or the other depending what permissions they have
- it’s useful to see what the placeholders in the message are before uploading
  a CSV, to make sure the CSV has the correct column headings

This commit re-adds the message preview with a simpler UI. Discussed with
@antimega and we both agreed that the speech bubble tails on the messages should
go.

app/templates/components/sms-message.html

@@ -1,4 +1,9 @@
-{% macro sms_message(body, recipient=None, name=None, edit_link=None) %}
+{% macro sms_message(
+  body, recipient=None, name=None, edit_link=None, input_name=None, input_index=None
+) %}
+  {% if input_name %}
+    <label class="sms-message-option" for="{{ input_name }}-{{ input_index }}">
+  {% endif %}
   {% if name %}
     <h3 class="sms-message-name">
       {% if edit_link %}
@@ -8,14 +13,18 @@
       {% endif %}
     </h3>
   {% endif %}
-  <div class="sms-message">
-    <div class="sms-message-wrapper">
-      {{ body|placeholders }}
-    </div>
+  {% if input_name %}
+    <input class="sms-message-picker" type="radio" id="{{ input_name }}-{{ input_index }}" name="{{ input_name }}" />
+  {% endif %}
+  <div class="sms-message-wrapper{% if input_name %}-with-radio{% endif %}">
+    {{ body|placeholders }}
   </div>
   {% if recipient %}
     <p class="sms-message-recipient">
       {{ recipient }}
     </p>
   {% endif %}
+  {% if input_name %}
+    </label>
+  {% endif %}
 {% endmacro %}