use a grade_tree_local_helper to expand grade_tree_local's (based on grade_tree) parameters without throwing a notice
brought fill_cats and fill_parents under the grade_tree_local object so could easily pass other portions of the object, most notably $this->mods which tells which items should be excluded because they're exclusive to group other than the current group
commented out the line that says, "Please wait while the table is loading"
added grade_tree_local_helper function so could pass more variables to grade_tree_local
coding changes in order to filter out grade items under group mode that are exclusively for a different group