Enhanced security module (including test).

The SHOGun2 authentication provider will now request a user from the database. The accountName of the user will be used as the principal in the authentication object.
Make the accountName of the User model unique.
Add findByUsername-method to userService.
Add basic security annotations to the CRUD service
Content initializer creates demo users and app.

For the demonstration of the ACL usage, some access control entries were made.