Audio effects improvements in version 0.7.8

We added some basic audio channel manipulations. We have had a Mono to stereo, which basically copied the left channel to the right. This was expanded to allow copying right-to-left. In addition, now you can swap the left and right channels to correct stereo inversion using Swap channels.

Next, we added Balance and Pan to affect the stereo "image." Both of these are keyframe-able. The difference is that Balance adjusts the apparent center, and Pan adjusts the left-right "position" of an individual channel.

Lastly, we fixed some of the SoX-based effects and removed some that were not fixable because either SoX removed them (Vibro) or they do not integrate well (Reverb and Pitch Shift) because they have time-related side effects.