templates: Base template for all applications

To show introduction and title of a module which will be available as
properties of a module.  This allows the setup process to show the
introduction to the application instead of a blank page.

plinth/templates/app.html

@@ -0,0 +1,33 @@
+{% extends "base.html" %}
+{% comment %}
+#
+# This file is part of Plinth.
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as
+# published by the Free Software Foundation, either version 3 of the
+# License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+#
+{% endcomment %}
+
+{% load i18n %}
+
+{% block content %}
+  <h2>{{ title }}</h2>
+
+  {% for paragraph in description %}
+    <p>{{ paragraph|safe }}</p>
+  {% endfor %}
+
+  {% block configuration %}
+  {% endblock %}
+
+{% endblock %}