Add custom template for 403 reponse code

plinth/templates/403.html

@@ -0,0 +1,38 @@
+{% 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 submenu %}
+{% endblock %}
+
+{% block content %}
+
+  <h2>{% trans "403 Forbidden" %}</h2>
+
+  <p>
+    {% with request_path=request.path %}
+      {% blocktrans trimmed %}
+        You don't have permission to access {{ request_path }} on this server.
+      {% endblocktrans %}
+    {% endwith %}
+  </p>
+
+{% endblock %}