Core/Loot: Fix master loot

Players will be able to open the loot window and see the items in case of master loot.
If the item is under threshold FFA applies, else the item becomes locked.

Also fix an exploit related to master loot item give.
Core/Loot: Implement round robin for under threshold items in case of master loot

Thanks @Shauren for pointing out
Merge pull request #11719 from Dehravor/master-loot

Core/Loot: Fix master loot
Core/Loot

* Master Looter cannot freely loot items under threshold
* Update round robin looter only if loot is not empty
* Fixed loot bag icon appearing in raid frames when loot method was not Master Looter
* Fixed changing loot method reseting current round robin looter
Core/Maps: Fixed incorrect difficulty markers shown on the interface inside Icecrown Citadel (always displaying normal mode)
DB/SAI: Fix "Badlands Enraged Rock Elemental" event spam
Closes #11802
DB/Creature: Remove 2 no longer existing mobs

Gal'darah Image and Ingvar the Plunderer Image where removed with the introduction of 3.3 weekly quests.
Scripts/Misc: Small code optimizations
Core/Commands: Handle "" as empty string argument

Fixes #11548
Core/Misc: Fix warning
Merge remote-tracking branch 'upstream/master'

Conflicts:
	src/server/scripts/Northrend/UtgardeKeep/UtgardePinnacle/boss_skadi.cpp