Recent changes in modinfo caused some regressions

Recent changes in modinfo (MDL-25981) have caused the $cm objects to stop providing $cm->context.

It breaks at least all the places were ratings are used because they rely on that:

mod/data/view.php: $ratingoptions->context = $cm->context;
mod/forum/lib.php: $ratingoptions->context = $cm->context;
mod/glossary/view.php: $ratingoptions->context = $cm->context;

There are also some other uses (12) of:

$PAGE->cm->context

But they continue working so we can keep them unmodified for now.

Going to fix the 3 broken places NOW, hopefully there aren't more places.

Ciao