MiscUtil: Added CERN LDAP plugin.

* Creates ldap_cern plugin that can be used to retrieve information from
  LDAP at CERN (it's faster than the LDAP module in bibcirculation due
  to the modified queries and more generic - it returns lists with all
  users that match the query, so the filtering can be done outside of
  this plugin).
Merge pull request #82 from switowski/ldap_cern

MiscUtil: Added CERN LDAP plugin.