WowAce

Hendrik Leppkes:
    - Add a fallback for GetNumDungeonMapLevels, which can return nil on the Legion Alpha.
    Minor intentionally not bumped since this change is only needed on the alpha,
    but would need a full data update to take effect, which would only add overhead on live.
    
    Reported by Gethe and MysticalOS on IRC, fix tested by MysticalOS.
    - Add the confirmed Draenor zone finale scenarios to the instance overrides
    - Add the proper Garrison Level 2 instance IDs
    Fixes ticket 5.