Use the official auth. user name of the LDAP authentication to propagate
user name changes to the OLAT fallback and WebDAV HA authentications

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)

Adapt calendar web service to not use the identity name, add a new user
authentications web service based on identity key, remove the advanced
properties controller

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.

Use an unique instance of the test session controller for every window
where a user has started a test. Theoretically, the user can now work on
the test from several different windows (with some restrictions).