Fix for the "too low music volume" in the first five chapters of the game : some of the tracks were very hard to hear in the first chapters, now it's fixed :)

Hotfix for the chapter "Power Up" : fix the missing track when you kill the Gargantua, now you have a part of Alien's main title that play at the end of the chapter when you take the train just before "On a Rail".
I also made a better mix of the track that play when you talk to the wounded guard at the beginning of the chapter.

- The chapters "Apprehension", "Residue Processing" and "Questionable Ethics" are now fully functional with the new soundtrack
- Addition of two new tracks :
Alien - Cat Nip
Alien Covenant - Command Override

- The chapter "On a Rail" is now fully functional with the new soundtrack
- Addition of two new tracks from the second opus :
Aliens - Ripley's Rescue
Aliens - Dark Discovery