Refactored codes according to new database

Updated entity class according to the new database structure.
Updated DAO according to the new database structure.
Added unique identifier for each user role when user logged in to
prevent overlapping users (e.g. previously when admin login, it sets
user attribute to admin, if a lecturer login, it will overwrite the user
attribute).
Added individual logout page to logout different type of user
(admin/lecturer/nurse) accordingly.
Created various protect.jsp to protect right page for right users
(admin/lecturer/nurse).
Updated codes according to new data type and fields used in database.
Added validation for practical group login and account creation
(duplicate user ID)
Added validation to check if only one scenario is activated