Uppgift 1:
	DataAccessLayer:
		getPastStudentsOnCourse(String)			- ändrad sql
		getCurrentStudentsOnCourse(String)			- ändrad sql
	View:
		btnFindCourseActionPerformed				- implementerat felmedelande
		btnDeleteRegisterCourseActionPerformed		- implementerat yterligare felmedelande
		btnDeleteRegisterStudentActionPerformed		- samma