Univention Corporate Server 4.2 erratum 179 (bugfix)

This update addresses the following issue(s):
* The styling of dialogs has been adapted to the new design.
* build-report.txt was removed from the debian package.
* The directory listing of /var/www/univention/ has been disabled.
* The Univention Blog has been added to the help menu entries.
* For privacy reasons the username is not stored anymore in a cookie but in a
  HTML5 local storage, to remember the last logged in user.