Completion condition: add a comment or make an annotation

[t-schroeder]

(Suggested by Michelle Doyle on https://moodle.org/plugins/mod_pdfannotator)

It should be possible to make the completion of a PDFannotator instance dependent on whether a student made a comment or created an annotation or asked a question.

Freehand drawings and text inserted into the PDF should probably not count. You can't ask questions with those annotations.