Extract strings from django templates

Also mark some strings translatable.

This commit violates hard string freeze after RC1 phase,
but this change only add new strings and allows translators
to translate strings which cannot be tranlated now.

Change-Id: Ia3b3889347c6ccb97488409f8409cb44d6a2586f
Closes-Bug: #1561203

babel-django.cfg

@@ -1 +1,5 @@
+[extractors]
+django = django_babel.extract:extract_django
+
 [python: **.py]
+[django: **/templates/**.html]

designatedashboard/dashboards/project/dns_domains/templates/dns_domains/domain_detail.html

@@ -3,7 +3,7 @@
 {% block title %}{% trans 'Domain Detail' %}{% endblock %}
 
 {% block page_header %}
-  {% include "horizon/common/_page_header.html" with title="Domain" %}
+  {% include "horizon/common/_page_header.html" with title=_("Domain") %}
 {% endblock page_header %}
 
 {% block main %}

designatedashboard/dashboards/project/dns_domains/templates/dns_domains/records.html

@@ -20,7 +20,7 @@
             </div>
         </div>
     <div class="nameservers_wrapper">
-      <h3>Nameservers</h3>
+      <h3>{% trans "Nameservers" %}</h3>
       <ul>
       {% for server in servers %}
         <li>{{ server.name }}</li>