Conditional audio module

[FurkanKambay]

Hey! So I'm using FMOD in my project and wanted to try out Graphy as well, but I also want to disable the built-in Unity audio module. I got errors when I did that because the code depended on it. So, here's one way of solving the issue using conditional compilation, letting users disable the built-in audio module and excluding all audio-related code.

This doesn't touch the prefab files so the audio-related fields are still serialized in them, which means if the developer decides to re-enable the audio module, they get those fields back (at least for the prefabs inside the package).

Thanks!