Scripts/Ulduar: Fix Algalon the Observer outro phase(fixes kill credit and some achieves).
DB/Creature: spawn Stabled Argent Warhorse

By Foldor, closes #11479, updates #11043
DB/Creature: Fix another trigger visible to players
Merge branch 'master' of https://github.com/TrinityCore/TrinityCore into ghbb
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