[Jouklik]

When merged this pull request will:

• Make Common track another volume for headphones
• Apply new headphones volume to vanilla radio and music
• Make Hearing track attenuation for headphones and making earplugs only equipment to lower it

This PR would make ACE track separate volume for headphones, because it makes no sense that putting helmet on would lower volume of radio on headphones, since these headphones are either bellow helmet or integrated into helmet. Tank crew or pilot helmets are going to have radio integrated into them, so putting them on would protect crew from loud outside sounds, while keeping radio loud and clear, so they can communicate. They had crew helmets with radio in them in WWII. 😀

Music is similar story. This won't change volume of music playing on speakers in 3D environment, only music played by playMusic, which is same as playing music in music player app on your PC. Using headphones volume for this is more suitable.

This PR won't change anything about volume of radio mods, since apparently these use one global volume. It's on them to implement separate headphones volume, if they wish so. It would be right step for more realism and immersion.

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