refactor Audio to remove requirement of AudioData
sensible initialization for Audio member variables
add packet headers and agent types for audio clarity
prepend audio packets from the mixer with a packet header
refactor constructor in AudioInjector
data sent to client from mixer must include packet header
correct some global references in Audio.cpp
spacing changes
remove extra space
comment cleanup for audioCallback
constantize the number of packets to discard for stats
constantize VOLUME_BASELINE in addProceduralSounds
constantize SOUND_PITCH in addProceduralSounds
spacing changes in Audio render
Merge pull request #317 from birarda/audio-refactor

refactoring Audio in interface and audio-mixer