MDL-32508 course: Add basic 'add a section' button at the bottom of the course page

With thanks to LUNS who provided this code from when I did it working
there.

course/addsection.php

@@ -0,0 +1,37 @@
+<?php
+
+// This file is part of Moodle - http://moodle.org/
+//
+// Moodle is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// Moodle 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 General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
+
+
+require_once(dirname(__FILE__).'/../config.php');
+require_once($CFG->dirroot.'/course/lib.php');
+
+$courseid = required_param('courseid', PARAM_INT);
+$course = $DB->get_record('course', array('id' => $courseid), '*', MUST_EXIST);
+
+$PAGE->set_url('/course/addsection.php', array('courseid' => $courseid));
+
+// Authorisation checks.
+require_login($course);
+require_capability('moodle/course:update', context_course::instance($course->id));
+require_sesskey();
+
+// Add an additional section.
+$course->numsections++;
+$DB->update_record('course', $course);
+
+// Redirect to where we were..
+redirect(course_get_url($course));