audio: 3D audio; sound propagation system

• 3D audio sources through classic source/listener model
• Sound propagation through the audio scene using the sector/portal model (similar to Wwise)
  • Including multiple path A* with path blending
• Direction, gain and effect smoothing to avoid audio jumps (using a simple IIR filter/smoother)

There are a few TODOs and loose ends to tie, namely:

• Downmixing/upmixing for various channel counts
• Some proper curves (at least a few predefined options) to drive distance attenuation on effects; currently the values are hardcoded
• Doppler effect

Other than that, after this MR gets merged, the audio module should be 95 % there and ready for tutorials/benchmarks.