clean-up commite
Add role information: Superuser, Admin and User.
To do authorization, but there is a lot of code duplication here.
Never mind, you do it later, next step is to do sorting and pagination.
refactored the persitence level, add two more tables
and refactor a lot of codes, which is previously involved with
`users_table`. Way to go.
Add pagination and sort to user/list method
Use maven to manage jars and project