Enhanced CRUD operations, fixed composite keys bug

- Schools and users are now correctly created in the way the application
  want it:
  -> On sign up, a user will generate two additional rows: a row for his
     roles as employee and a row for his role as student
  -> On school creation, a user will correctly be his founder, and will be
     the only one who can perform update and destroy operations on it
- Enforce security for SchoolController and UserController:
  -> Redirect user on a 404 error page if the ID in the REST-like URL is
     wrong
  -> Redirect user on a 403 error page if he is not allowed to do the
     current operation on the current entity
  -> Updates must be valid
- Modified security configuration style from "implementation style" to
  "abstract class style" with support classes provided by Spring
- Modified views to better accomplish their roles (added forms)
- Modified some DAOs and their related services to add some find functions
- Added a service to find differents roles for employees in a school
- Deleted an old file for authentification handling, finally useless
- Removed some additional useless @XMLRootElement annotations generated
  before
- Should now delete validation annotations in entities and put them in
  forms objects (entities must represent DTOs and nothing else like
  validation)