LDEV-3115 Fix group removal on LD save in authoringIt seems that Hibernate does not like having entities violating unique keys in one collection. Even for a while and even though afterward the collection contains only unique entities.
LDEV-4746 Rewrite QB question insert triggerIt should accept existing UUID if it is provided. It is important when importing LD from zip and when there are same questions used in several activities, for example TBL RAT.
LDEV-5423 Complete Flux on all subscriptions terminatedAlso:* use separate and configurable task executor for async requests* introduce backlog pressure strategy for Fluxes* synchronise access to Flux mapping* add logs
