(cherry picked from commit 4fa2427e)

(cherry picked from commit 01470b39)

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

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.

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).