Cleaning up the codes for Prof's & Student's login

1) Split check_login_success.php into 3 different files to cater to
different users.
(a) checkLogin.php to check if student's/prof's username matches with
password
(b) loginSuccess_Student.php for students after login successful
(c) loginSuccess_Prof.php for profs after login successful

2) Edited login.php and wrongLogin.php
(a) Now users can choose their domain - either 'Prof' or 'Student' with
radio buttons.
(b) Changed the check_login_success.php to checkLogin.php in both files