Add user type

[georgebejan]

Based on: #5

Currently the User entity has no reference to any roles.
An user can have the following roles:

• PF/REGULAR (persoana fizica)
• Public authority
• Public utility

Add the information about user role to the User entity. One user can have only one role.
Update the role which is set to the UserPrincipal after login.

[rmitoi]

I'd like to work on this