@package: Listing

Method: Returns message if groups are not set to Public

Method: Show selector for price type.

Method: This function fill filter the table listing items by the selected Price Type.

Method: Show Price Type column.

Method: Called via the WordPress init action hook.

Method: Call via the WordPress load sequence for admin pages.

Method: Listing table query vars

Method: Show Group Course Users column.

Method: Filter the main query listing by the course_id

Method: Public constructor for class