bug#64160: master; Implement various enhancements in ldap.el and EUDC

[Jens Schmidt]

This is a tracking bug for various enhancements in ldap.el and EUDC,
please do not close until further notice.

Some of my intentions:

- Add an additional front-end to EUDC, more user-friendly and dwimmy
  than `eudc-query-form'.

- Add commands in EUDC to traverse the management hierarchy of
  some organization.

- Extensions in particular to ldap.el to support above:

  + extension of the WITHDN parameter, since that is often (?) used
    to establish manager <=> reports relations

  + modernization of the code in `ldap-search-internal' to
    read LDAP attributes with less temporary files being created

  + option to return attributes in some specified order

This is also related to bug#64089, which I thought to be the starting
point of these enhancements.