Force the nick name to be unique with a DB constraint, with an issue
where the user name for the OLAT token is the auto generated identity
name after changing the password

REST add a user search by external id, remove the login value of UserVO
if identity name are automatically generated

Adapt LDAP for auto/manual generated id. name, add unit tests for
special workflow (user which are created without authentication and get
LDAP token afterwards on login)

Login happens only with authentication informations, identity name is
now only used for legacy directory name. User name of authentication can
be changed. LDAP users can be imported with LDAP::ldapUid. Users can be
imported in courses, groups... with First name last name.

Implement a CSRF token to protect a little more against CSRF attack.
Enhance the UI framework to allow opening a link in a new browser
window.