Improve WMO vertex color and lighting

[fallenoak]

Many WMOs, particularly WMOs found in Northrend (but also many old world WMOs), have vertex coloring and lighting issues that leave much to be desired.

Progress

• Implement FixColorVertexAlpha
  The client, it turns out, modifies the on-disk MOCV values a fair bit when loading WMO groups. We should replicate this modification in Wowser. This will fix the missing glow around fireplaces in old world inns / houses, the undersaturated glow in blacksmith WMOs, and likely several other color issues.
• Properly handle baseAmbientColor
  Likely baseAmbient is always supposed to be added when shading WMO groups, and flag 0x02 is not about skipping or adding it, but is rather about specific behaviors when modifying MOCV colors in FixColorVertexAlpha.