Set LastSuccessSynchronization timetamp when synchronize groups

 - new attribute group_def_lastSuccessSynchronizationTimestamp which is
   set only when exception message is equal to "OK". OK means that no
   exceptio was thrown in the middle of synchronization.
 - if this attribute definition is not exists, only log this to
   log.error

 NEED TO BE DONE BEFORE MERGE:
  - should create new attribute:
   - String, group_def_lastSuccessSynchronizationTimestamp
  - add information about new attribute to changelog