DB/Creature: Opus must have 4 random models

Closes #12404
DB/Creature: Update some wrong creature_template_addon
Core/Instances: Enable automatic changing dungeon difficulty to a lower one when currently selected difficulty does not exist for entered instance
Fix typo on 077c6e1
Fix typo on bb8922a
Core/Battleground:
* added a possibility to reload battleground templates
* cleaned up the template structure
* use mapids from BattlemasterList.dbc to calculate random bg
DB/Quest: Fix remaining issues with Argent Tournament Chaining

By dr-j, closes #12455
DB/Gameobject: Template updates for gameobject 1721 (Locked ball and chain)
DB/Quest: Dissension Amongst the Ranks...

By dr-j, closes #4826
Merge branch 'master' of github.com:TrinityCore/TrinityCore into 4.3.4

Conflicts:
	sql/base/auth_database.sql
	src/server/game/Battlegrounds/Battleground.h
	src/server/game/Battlegrounds/BattlegroundMgr.cpp
	src/server/game/World/World.cpp