new(updateId:String, serverId:Null<String>, serverIdBy:Null<String>, localId:Null<String>, chatId:String, senderId:String, timestamp:String, reactions:Array<Reaction>, kind:ReactionUpdateKind)
finalchatId:String
finalkind:ReactionUpdateKind
finallocalId:Null<String>
finalreactions:Array<Reaction>
finalsenderId:String
finalserverId:Null<String>
finalserverIdBy:Null<String>
finaltimestamp:String
finalupdateId:String
getReactions(existingReactions:Null<Array<Reaction>>):Array<Reaction>