fixed naming of monitor threads (no impact)

* has no impact to code behaviour, but makes logs more informative
fully reinitialize KWS ranker on every reload

* reinitialize: list of lookup keys, api constraints
event dispacher to inform KWS about DASMaps reload

* simple generic event dispacher function in DAS.utils.utils
* event in das_mapping_db and handler in KWS
improved docstring for eventsubscription
Merge pull request #4066 from dmwm/kws_ranker_reload_fix

Kws ranker reload fix