Store user groups and properties as session data * stop retrieving them systematically, only when need, * reimplement session synchronization hooks with some cleanups along the way, * cleanup call to set language: not needed from the base request nor from the server side, only for the web request (on the server side, language is necessary only for notification and such code should set it explicitly). There is still a XXX remaining about one can only "enter" a connection once and this is a problem in some cases. IMO, this restriction could be removed. Closes #13500113.

The personal information describing a User can be modified using the edit form
of the user. You can access it through the dropdown-menu under the link on the
top-right of the window, labeled by your login. In this menu, click the
"profile" link to go to this form.

Each user can as well customize the site appearance using the "user's
preferences" link in this menu. This will show you a form to configure which
boxes are displayed, in which order, etc...

.. image:: images/userprefs