Forsaken Sentinels

Adds a duo fight against Phantom and Second Sentinel. To access the fight, visit the Exhaust Organ after waking Second Sentinel with the Cogwork Heart and before defeating Phantom.

The mod makes small changes to the Exhaust Organ, as well as modifying the intro, phase change, and end of the boss fight.

~It is known that defeating Second Sentinel before Phantom stops the background music for the remainder of the fight. This may or may not be fixed in the future.~