AHBot related fixes

Fix rebuild command requiring a dummy value

Fix ahbot config to normal

Fix sellprice setting in core. Closes #13425
DB/Item: Northrend Mystery Gem Pouch (3.3.5)

* This is probably only valid for 3.3.5 as item is marked as no longer available in game and last comment on wowhead is from 4.1.0 saying item is now worthless, was added in 3.2
* Remove northrend rare gems for emblem of heroism from Lhara and replace with this item
DB/Misc: Zone Wide Texts
DB/Misc: Short John Mithril / Arena Treasure Chest

* Remove permament spawn of Arena Treasure Chest 
* Script Short John Mithril to start wp at start of event, say his 2 lines (1st zone wide) and summon Arena Treasure Chest
Merge pull request #13440 from Rochet2/ahbot

Core/AH: AHBot related fixes
Scripts/Ulduar: Fix Ignis' Slag Pot periodic ticks and enable achievement "Hot Pocket"
Merge branch '3.3.5' of https://github.com/TrinityCore/TrinityCore into master_revamp