Add sound effects

[mminer]

I don't think we need to spend too much time on this. Unless sound plays a meaningful role in the gameplay, which could be interesting to explore.

[mminer]

I added a bundle of sound effects from Kenney's RPG Audio in f975e54 and AudioService in e38f3fc. To play a sound effect we'll run something like this:

Services.Get<AudioService>.PlaySoundEffect(footsteps);