Univention Corporate Server 4.4 erratum 612 (bugfix)

This update addresses the following issue(s):
* It is now possible to navigate to an UMC module without the overview
  of all UMC modules and have only that UMC module open.
  This can be achieved for example with:
  https://fqdn/univention/management/?overview=no#module=top
* The Content-Security-Policy for UMC and its login dialog is now
  configurable via the umc/http/content-security-policy/.* and
  umc/login/content-security-policy/.* UCR variables.
  The X-Frame-Options default header has been replaced
  with the Content-Security-Policy frame-ancestor setting.
* Some preparations for the upcoming "Univention Portal" app have
  been made.
* The UMC-Server components are now Python 3 compatible.