Rename ‘generate preview’

‘Print a test letter’ seems to be closer to what people’s expectations
of what this feature does are.

The word ‘generate’ sounded too much like something the system was
doing, rather than something you, the user, were doing.

app/templates/views/check.html

@@ -178,7 +178,7 @@
       {% if template.template_type != 'letter' or not request.args.from_test %}
       <input type="submit" class="button" value="Send {{ count_of_recipients }} {{ message_count_label(count_of_recipients, template.template_type, suffix='') }}" />
       {% else %}
-        <a href="{{ url_for('main.check_messages_preview', service_id=current_service.id, template_type=template.template_type, upload_id=upload_id, filetype='pdf') }}" download="download" class="heading-medium">Download as PDF</a>
+        <a href="{{ url_for('main.check_messages_preview', service_id=current_service.id, template_type=template.template_type, upload_id=upload_id, filetype='pdf') }}" download="download" class="heading-medium">Download as a printable PDF</a>
       {% endif %}
       <a href="{{ back_link }}" class="page-footer-back-link">Back</a>
     </form>

app/templates/views/send-test.html

@@ -18,7 +18,7 @@
     Example text message
   {% else %}
     {% if template.template_type == 'letter' %}
-      Generate preview
+      Print a test letter
     {% else %}
       Send yourself a test
     {% endif %}

app/templates/views/templates/_template.html

@@ -14,7 +14,7 @@
         </div>
         <div class="{{ 'column-half' if template.template_type == 'letter' else 'column-third' }}">
           <a href="{{ url_for(".send_test", service_id=current_service.id, template_id=template.id) }}" class="pill-separate-item">
-            {{ 'Generate preview' if template.template_type == 'letter' else 'Send yourself a test' }}
+            {{ 'Print a test letter' if template.template_type == 'letter' else 'Send yourself a test' }}
           </a>
         </div>
         {% endif %}