Scripts/Onyxia Lair: small rework

- fix crash on boss death
- avoid abusing during phase switch
- added better facing through trigger
- corrected some timers
- corrected inhabit type
- cleanup and inheriting some BossAI functionalities instead of custom stuff

sql/updates/world/2014_09_01_01_world_onyxia.sql

@@ -0,0 +1,2 @@
+UPDATE creature_template SET InhabitType = 5 WHERE entry = 10184;
+UPDATE creature_template SET InhabitType = 5 WHERE entry = 36538;