MDL-20264 work in progress on grading evaluation support

Also fixes small bugs in workshop api constructor and in using "scales"
instead of "scale" for the core table name.

mod/workshop/view.php

@@ -160,7 +160,7 @@ case workshop::PHASE_EVALUATION:
     $page       = optional_param($pagingvar, 0, PARAM_INT);
     $perpage    = 10;           // todo let the user modify this
     $groups     = '';           // todo let the user choose the group
-    $sortby     = 'submissiongrade';   // todo let the user choose the column to sort by
+    $sortby     = 'assessmentgrade';   // todo let the user choose the column to sort by
     $sorthow    = 'DESC';        // todo detto
 
     $data = $workshop->prepare_grading_report($USER->id, $groups, $page, $perpage, $sortby, $sorthow);