admin: Improvements to micropub endpoint's photo handling. - Add `.jpg` extension to photos that don't have any extension. - Add photos in the config section instead of the body, so that the layout can put them in separate `u-photo` tags.

{% set title = 'Micropub Endpoint' %}

{% extends 'layouts/master.html' %}

{% block content %}
<p>This is PieCrust's Micropub endpoint.</p>
{% endblock %}