Corrected the function to change between pages of the students list in the teacher portal.

Also, in the students list, changed the student's registration number with the student's username.
Merge pull request #519 from cbartol/ticket/rt#417567

Corrected the function to change between pages of the students list in the teacher portal.
Also, in the students list, changed the student's registration number with the student's username.

close #518