Univention Corporate Server 4.4 erratum 528 (bugfix)

This update addresses the following issues:
* Internal change: the UCR templates of are now python3-compatible.
* Do incremental updates for attribute `uniqueMember` of groups: Changes
  trigger the slapd overlay module `memberof`, which then needs to update all
  users of the group. This is inefficient with MOD_REPLACE as the overlay
  then has to walk over all users instead of only the added/removed users.
  During the walk each user object is touched and triggers a sub-transaction
  in OpenDLAP. With slow disks this even can lead to TIMEOUT errors as the
  LDAP connection is closed after 5 minutes by default.