Generation of active events by handlers

[Limraj]

Description For a given group of errors in the operation of the Event Handler, a maximum of one active event should be created.

Reason Currently, Evnet Handlers generate an event for every error, even if it's the same error. Which, in extreme cases, may lead to the uncontrolled generation of many events, which in turn leads to the application slowing down and may even lead to its failure.

Spec Scada-LTS version: <=2.6.18