Make package filters for sections work (#6576)

Make package filters for sections work (#6576)

- Add support to FAI_get_packages function to filter by section,
  by adding a new attribute exclude_sections which allows the
  specification of an array with sections as keys (and arbitrary
  values).
  (This way its possible to create the array with array_filter and the
  existing package_sections array in class_faiPackageEntry)
- Extend class_faiPackageEntry to hand the list of unselected sections
  to FAI_get_packages
- Extend class_faiPackageEntry to keep the state of the section
  selection on page reload

git-svn-id: https://oss.gonicus.de/repositories/gosa/branches/2.6-lhm@20706 594d385d-05f5-0310-b6e9-bd551577e9d8