Massive update:- User anthen servlet 
                    1. change in SQL string to query for password and  
                       username if that username have password not
                       same as input it should throws SQLException
                    2. improving security on redirect to login page
                       using requestDispatcher instead of sendRedirect
                       (hidden login page URI)
                - Log out Servlet
                    1. changed to requestDispatcher due to User anthen 
                       servlet(number 2)
                - User comment servlet
                    1. changed statement to preparedStatement due to  
                       security(prevent SQL injection string)
                - User register servlet
                    1. changed statement to preparedStatement due to 
                       security(prevent SQL injection string)  
                    2. changed sendRedirect to requestDispatcher for 
                       prevent user who want to view register fail page 
                       directly