Spells → Battlegrounds Relation

File in server/game/Spells	Includes file in server/game/Battlegrounds
Spell.cpp	Battleground.h
Auras / SpellAuraEffects.cpp	Battleground.h
SpellEffects.cpp	Battleground.h
SpellEffects.cpp	BattlegroundMgr.h
SpellInfo.cpp	Battleground.h
SpellMgr.cpp	BattlegroundMgr.h