Fix: Query hardened for the several model class

[Anindra123]

• CourseModel.php

  • Added abspath check
  • In get_courses added check for excludes id array and post status parameter and used prepare in clause
  • Utilized cap manage_options instead of administrator

• models/EnrollmentModel.php

  • Added abspath check
  • In get_enrolled_data added check for status and course id post type

• models/OrderModel.php

  • Added abspath check
  • In create_order after catch no rollback query was running
  • In get_refunds_by_user the $user_id was placed with direct interpolation with no prepare query check