Student Charges

- StudentCharges Servlet: retrieve students, loop through students and
set their charges to the values from the text boxes
- User entity: added a constructor that sets the values of students
- studentCharges.jsp: tested creating a student  as well as gave the
text boxes for the charges names that made them more individual (instead
of classname_charge, it is called studentid_classname_charge)
- Error when pressing the submit button:
"Persistence Manager has been closed"