Add 3D character model preview to character creation screen

Render an animated M2 character model in the creation screen using a
dedicated CharacterRenderer with an offscreen FBO. Preview updates on
race/gender/appearance changes, supports mouse-drag rotation, and
composites skin, face, hair scalp, and underwear textures from
CharSections.dbc. Extracts getPlayerModelPath() to a shared free
function in game/character.

include/game/character.hpp

@@ -133,5 +133,10 @@ const char* getClassName(Class characterClass);
  */
 const char* getGenderName(Gender gender);
 
+/**
+ * Get M2 model path for a given race and gender
+ */
+std::string getPlayerModelPath(Race race, Gender gender);
+
 } // namespace game
 } // namespace wowee