MDL-28505 Backup: Asynchronous backup and restore

This patch adds asynchronous backup and restore functionality
to Moodle. This is an optional feature and is not enabled by
default. It can be enabled by site administrators.
Asynchronous backup and restores are actioned by the Moodle
adhoc task API. The progress of backup and restores is
displayedin the Moodle UI.  Users can also be sent a message
when a backup or restore operation completes via the
Moodle messaging API.

course/view.php

@@ -5,6 +5,7 @@
     require_once('../config.php');
     require_once('lib.php');
     require_once($CFG->libdir.'/completionlib.php');
+    require_once($CFG->dirroot . '/backup/util/includes/backup_includes.php');
 
     $id          = optional_param('id', 0, PARAM_INT);
     $name        = optional_param('name', '', PARAM_TEXT);
@@ -243,6 +244,10 @@
     $PAGE->set_heading($course->fullname);
     echo $OUTPUT->header();
 
+if ($USER->editing == 1 && async_helper::is_async_pending($id, 'course', 'backup')) {
+    echo $OUTPUT->notification(get_string('pendingasyncedit', 'backup'), 'warning');
+}
+
     if ($completion->is_enabled()) {
         // This value tracks whether there has been a dynamic change to the page.
         // It is used so that if a user does this - (a) set some tickmarks, (b)