Changes

Added the UserEJB and the Mail functionality
Added the UserEJB to use with the UserJPA to do some little things like
create, modify, delete and find/findAll. Also, when a new user is
created, we have to send a confirmation email, so we will use the
Wildfly mail system to do so. All od the Mail info is in
'PROJECT_DOCUMENTATION.md'. The UserJPA and UserPlayerJPA were modified
to have 1 more attribute.