Core/Summons: Implement summon groups system to be able to summon multiple NPCs at once without need of hardcoding the positions. Almost all hardcoded positions can now be moved to DB.

Thx to @Shauren for his help.
Merge pull request #9280 from horn/summons

Core/Summons: Implement summon groups system to be able to summon multiple NPCs at once without need of hardcoding the positions. Almost all hardcoded positions can now be moved to DB.