Scripts/UtgardePinnacle: King Ymiron

- Updated to EventMaps
- Replaced manual summons with proper spells
- Fixed glitch where boss would resume fight/run back to his main target before the ancestor summon roleplay was over (it might still need few adjustments i.e fire on boat is currently missing)
- Implemented damage calculation for spell Dark Slash (http://www.wowhead.com/spell=48292) as previously the spell would do no damage and it's BasePoints is 0