Dataform ratingmdl field adjustments.

Several adjustments are required:

• Aggregate display of non-numeric scale displays the numeric rather than textual rating value.
  • Normalizing aggregate display via a new method dataformfield_ratingmdl::get_rating_display_aggregates(). The method will return '-' for empty aggregates.

• Ajax rating doesn't update the gradebook when the field is used in calculated grading.
  • Get user values doesn't return the expected values. This method is required for calculated grading. Currently done by implementing interfaces\grading but will be replaced with helper\contentperuser.

• Content and display break after changing scale in the field's setting.
  • This required updating all the field's ratings if changing the scale.
  • It should adjust upper limit (e.g. new scale has less items than old scale).
  • It should delete redundant ratings (e.g. point scale can have 0 ratings but non-point scale cannot).

• There is no way to display raw rating aggregates.
  • This may be needed e.g. for export or for custom displays such as star rating.
  • Currently there are aggregate patterns, e.g. [[fieldname:max]], which are rendered with extra html for ajax updates. These patterns will be replaced with e.g. [[fieldname:view:max]] (upgrade required). The original patterns will display raw values of the aggregates.

• Ajax rating and rating display are not available when editing the entry.

• Aggregate display is not updated when reseting a rating when there is only one rating.
  • This is b/c the javascript updates aggregates only if there are ratings, and when a single rating is reset it is deleted before updating the display and so the display is not updated.