Univention Corporate Server 4.0 erratum 90 (bugfix)

The following issues are addressed by this update:
* Displaying of the UMC reload dialogue has been adjusted.
* The automatic selection of the first item in a list widget (e.g., in
  the installed system locales in language settings) has been removed.
* The positioning of the "back to overview" header button has been adjusted.
* The default search button has been adjusted to be smaller and to only
  contain an icon instead of text.
* The UMC header menus have been adjusted in their positioning on small
  screens and they have been styled with icons.
* Methods for resetting UMC modules and renewing a session have been added.
* Notifications must now be closed via a close icon.
* Pop-up dialogs that need no verification now have a close icon.
* The label for module buttons is now centered if there is enough space.
* The number of parallel and open request in the UMC webserver has been
  raised and can now be configured via the UCR variable umc/http/maxthreads