Univention Corporate Server 4.1 erratum 130 (bugfix)

This update addresses the following issue(s):
* univention-register-apps now uses the new appcenter API and has been
  deprecated.
* An error during loading the appcenter cache has been fixed which prevented
  using the appcenter when the cache file was corrupted.
* Malformed files for meta information could cause the App Center to show a
  traceback. This has been fixed, those files are ignored now.
* Upon upgrading the App Center software package, the App cache could get
  outdated. This caused an error in the App Center in some cases.