Mange:
	- Added alternate power bar tracking for onyxia in the Nefarian encounter in BWD.
	- Boss health bars are now added when INSTANCE_ENCOUNTER_ENGAGE_UNIT fires instead of doing it manually via boss IDs.
	- Added new plugin to handle the new alternate power bar. It can disable the default one and only show it on the multi-purpose bars, or show both. It will also let the player set the position of the default alternate power bar.
