Converting iOSSonic from a C++ class to Obj-C class

This will allow us to retrieve the song file within iOS::addAudioObject
rather than leaving this up to the ViewController. Still need to:

(1) Generalize file-getting for any file (hard-coded right now)
iOSSonic::addAudioObject now gets filepath from mainBundle
removed unused bitDepth var in addObjToMix
added timing into addAudioObjToMix

still need to finish it though and print runtime along with
thread number to debug issues with multithreaded mixer playing > 1
audio object.