More XAct Improvements

This PR has a bunch more XAct runtime improvements:

 - We now obey pitch for non-complex sounds.
 - We gracefully handle missing wavebanks like XNA does.
 - We now do proper weighted randomizations.
 - Added volume and pitch variation play event support.
 - We now read the sound priority.
 - We now read panning randomization.
 - We now read standard flags for simple playback events.

Still more to do, but this gets us much more compatible with XAct features.