Checkpoint commit for OPENDJ-1288 : 
  Migrate I18n and logging support to i18n framework and SLF4J

* Final step for simplification of logging levels, in order to keep only ERROR, 
WARN, NOTE, INFO and DEBUG
** Update Severity class to keep only the wanted levels
** Remove remaining references to levels to delete in message properties
 files and config.ldif 

* Move all publishers classes to org.opends.server.loggers package :
 AccessLogPunlisher, ConsoleDebugLogPublisher, DebugLogPublisher,
 ErrorLogPublisher, HTTPAccessLogPublisher, LogPublisher
 ** Update of corresponding XML configuration files referencing the
 classes  
 
* Reduce visibility of classes and methods in org.opends.server.loggers 
 package when applicable