OPENDJ-1444 CR-4537 Remove previous cookie from storage of ChangeNumberIndexDB

[Note: real merge of all changelog.file package content and ChangelogBackend to be done 
 in one shot in a future commit]

* Implement a new matching strategy for cursors : LESS_THAN_OR_EQUAL_TO_KEY
   for both je and file-based implementations

* Replace the previous cookie by the usage of an ECLMultiDomainDBCursor generated 
   with the medium consistency CSN as start point and the 
   LESS_THAN_OR_EQUAL_TO_KEY strategy
   in classes ChangeNumberIndexer and ChangelogBackend

* Remove storage of the previous cookie in the log for both je and file-based
   implementations