Development - Levels instead of parent/grandparent for courses

[Nullmann]

Legacy code from Moodle Analyst included SQL-Queries which retrieved the parent and grandparent of courses. This resulted in errors when the courses were not structured /semester/department/course.

Also includes additional features:

• Dropdowns are sorted as set in course management (including only visible categories)
• Last Login and idnumber for users is displayed
• Upgraded DataTables and removed unnessesary files
• Some styling
• Many bugfixes (not technically a feature)