Merge pull request #289 in ZP/z-push from feature/ZP-972-allow-backends-enable-device-or-user-logs to develop

* commit '74efedde':
  ZP-972 Fixed @access.
  ZP-972 Implement ZLog::SpecialLogUser() to be called before authentication is completed to force the generation of a user log, fixed method descriptions, use Log::unauthMessageCache for all unauthenticated users, fixed ZLog dependency in PrintWBXML, removed ZLog::RequestHeaders(), removed ZLog::SetSpecialLogUsers(), removed ZLog::EnableDeviceLog().
  ZP-972 Add request header also to device specific log, by moving it from index.php to protected method ZLog::RequestHeader and calling it from ZLog::Initialise and ZLog::EnableDeviceLog.
  ZP-972 Use deviceid and authuser from Logger in zlog instead of getting them from Request. Renamed setLogToUserFile to SetLogToUserFile and added it as public to the abstract Log class. Renamed WbxmlDebug to IsWbxmlDebugEnabled. Fixed typos in function descriptions. Replaced tabs with spaces.
  ZP-972 fix WBXML is not logged for LOGUSERLEVEL >= LOGLEVEL_WBXML, if LOGLEVEL < LOGLEVEL_WBXML and $specialLogUsers is not already defined in config.php, because enabled on runtime via ZLog::EnableDeviceLog() or ZLog::setSpecialLogUsers().
  ZP-972 allow backends to enable device or user specific logging.