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 'base/base.html' %}

{% block title %}{% trans %}Error {{error_code}}{% endtrans %}{% endblock %}
{% block body %}
{% trans %}An error occured while trying to access the resource.{% endtrans %}
{% endblock body %}
{% block footer %}{% endblock %}