MDL-51179 Atto: Extend autosave fix to cover text changes

Added new functions to editor api - set/get_text so the
original form text can be determined from an editor.

When calling use_editor() you should first call set_text() with
the text that will be inserted in the form element.

There is also a new scheduled task for cleaning Atto autosave drafts.

question/behaviour/rendererbase.php

@@ -82,6 +82,7 @@ abstract class qbehaviour_renderer extends plugin_renderer_base {
 
         $commenttext = format_text($commenttext, $commentformat, array('para' => false));
 
+        $editor->set_text($commenttext);
         $editor->use_editor($id, array('context' => $options->context));
 
         $commenteditor = html_writer::tag('div', html_writer::tag('textarea', s($commenttext),

question/type/essay/renderer.php

@@ -236,6 +236,7 @@ class qtype_essay_format_editor_renderer extends plugin_renderer_base {
         list($draftitemid, $response) = $this->prepare_response_for_editing(
                 $name, $step, $context);
 
+        $editor->set_text($response);
         $editor->use_editor($id, $this->get_editor_options($context),
                 $this->get_filepicker_options($context, $draftitemid));