Core/Players: On CanRewardQuest, use the same item dest vector for all potential rewards
Scripting/Utgarde Pinnacle: Fix visual during Svala's transformation
Scripts/Halion: Fixed Soul Consumption's pull effect.

Thanks to Winterfell for pointing out the issue.
Core/Entities: correct creature damage, offhand damage should work too
* todo: some creatures need dmg_multiplier update in creature_template
DB/Spells: remove duplicate/invalid entries from spelldifficulty_dbc
* For new entries: use spellid0 as id to avoid conflicts with dbc file
DB/Spells: correct more spelldifficulty_dbc entries
* add log message to find wrong entries
Core/Threading: Handle CMSG_ZONEUPDATE only in WorldSession update - changing zones triggers changing chat channels, what is not a thread safe operation
Scripts/HoS: update Maiden of Grief
Core/Movement: Fixed vehicle passengers disappearing clientside

Closes #11411
Misc:

* Tools: Fixed a compile warning
* Commands: Fixed npcflag format in .npc info
Core/Entities: add some log messages in CheckCreatureTemplate
* Happy Error Spam
DB: update some creature templates
DB/Creature: update more creature templates
Scripts/BloodFurnace:
* cleanup InstanceScript
* fix broggok poison cloud

Scripts/Naxxramas/Grobbulus:
* fix poison cloud
* fix mutating injection
Fix build
DB/Spawns: remove duplicate NPCs on Zeppelin from Orgrimmar to Thunder Bluff

Closes #11420
Core/SAI: drop unneeded code
Scripts/PoS/Garfrost: cleanup saronit blocks after death
Core/Battlefield: some codestyle changes
Core/Spells: Fix potions cooldown in combat

Fix a cooldown issue related to potions allowing Players in combat to use more than 1 potion in a row, especially with high latency.
This also fixes an exploit about using infinite potions in combat just by skipping the client-side check.
The original implementation c064c2e2e1eebd43b273365583dd181293bafa22 was missing a check in Spell::CheckCast() about this particular case since Potion cooldown is added only after the Player goes out of combat.
Fixes #1259 .