remove one todo and added some comment

updateWithReferenceToExistingStudentRecord method added
some comments added for studentlogic

some comments added for studentlogic
refactoring and comment updated

change upon request; refactoring
change of method name

shorten the method name
added test for student registration email

students in course will not be covered
add for for sendingInviteForCourse

enrollStudentsInprogress
change ts msg
Merge remote-tracking branch 'origin/master' into Issue1949
Merge remote-tracking branch 'origin/master' into Issue1949
moving tests from logic test to studentLogicTest
add comment as marking for later work
adjust the way to add a new student
Merge remote-tracking branch 'origin/master' into Issue1949
some refactoring and fix of test fails
adjustment for some todos in studentslogic
remove duplicate code
remove duplicate code
Merge branch 'Issue1949' of https://github.com/TEAMMATES/repo into Issue1949
remove duplicate code

seems the test method is doing something that is completely unnecessary
to me
refactoring of testGetTeamsForCourse