Add idle.wav option

[NoSloppy]

This is a proposal for playing an idle.wav, mirroring idle.bmp image behavior.
I’m not sure this is the best way to do this, but I gave this a shot, and it seems to work well.
The feature is enabled with #define ENABLE_IDLE_SOUND and plays a sound named idle.wav whenever the blade is off.

Currently, SB_Off() sets idling_ to true, and after retraction (and postoff if it exists) sounds are finished playing, it starts playing idle.wav by triggering it from Loop().

Then idling_ gets set to false at ignition and when IDLE_OFF_TIME expires (when OFF_IDLE) and it stops playing.

[profezzorn]

Apart from how it's implemented, what is it for? who needs it? And I wonder if it would be better to use a prop that is always on, but has one alt mode for "on" and another one for "off" would be better?

[NoSloppy]

Apart from how it's implemented, what is it for? who needs it? And I wonder if it would be better to use a prop that is always on, but has one alt mode for "on" and another one for "off" would be better?

Most suggestions I got were regarding other props besides sabers. Plasma packs, Tron Discs, shelf display with ambiience, etc...
I don't disagree an "always on" prop could do something like this, I just thought that since there's an idle image that plays that this could be small addition to enable with a define and having the file exist.
This could go to a back burner for sure.