file (discover): new discovery page: the discovery page will show service, own devices and roster contact devices offering file sharing. An extra field allow to enter free jid. Added a small message in photo/discover.html has photo album discovery is not yes implemented. New block and images macros.

{% extends 'error/base.html' %}

{% block body %}
<h1>{% trans %}Not Found{% endtrans %}</h1>
<p>{% trans %}Sorry, we can't find the resource you are trying to access.{% endtrans %}</p>
{% endblock body %}