Route Cart Sounds Through The New Audio Manager

[Cheeseness]

Cart sounds are currently not played via @thegsm's new audio manager ( fdae830 ). Making them do so will make them respect volume control ( #193 ) and so forth.

[osse101]

SoundManager needs some additions to be able to handle acceleration/skid sounds because they are point sounds, looped, and updated per frame. Right now it seems like the audio source creation should be moved to SoundManager, but give CarAudio a reference that they can update. And poll SoundManager for sound state.

Not unreleated, the audio listener is on the camera and skews sounds as the cam moves. I'm thinking on the character is the place to put it instead.

[ErikBehar]

true soundmanager is not quite setup to handle 3d sounds too well at the moment. On a shorter term you could check with SoundManager flags to see if sound is muted or not and volume, before you play the 3d sounds. On a longer term, we could add more ways for the soundmanager to also handle 3d sounds well.