Add size queries in backend object lists.

[pithos] / pithos / api / templates / containers.xml

<?xml version="1.0" encoding="UTF-8"?>
{% load get_type %}
<account name="{{ account }}">
  {% for container in containers %}
  <container>
  {% for key, value in container.items %}
    <{{ key }}>{% if value|get_type == "dict" %}
      {% for k, v in value.iteritems %}<key>{{ k }}</key><value>{{ v }}</value>
      {% endfor %}
    {% else %}{{ value }}{% endif %}</{{ key }}>
  {% endfor %}
  </container>
  {% endfor %}
</account>