added Mixer interface
added first version of an AudioMixer implementing the Mixer interface
fixed issues in AudioSample and now start looping itself once it's loaded
made AudioContext a global variable in main.js as it was causing weird DOM exceptions when wrapped into a RequireJS singleton.
Furhtermore implemented the load/unload/tune methods in the AudioMediaObject and apply the values to the AudioEffects. The effects base class takes care of calculating the wet_value and calls a setWetLevel method on the effect that should be implemented by each subclass. It is important to note that each audio effect has an input and output by default (inherited) but has to take care of doing his own thing and connecting everything in-between.
added audio file for testing purposes. Source for it can be found here: http://freesound.org/people/acclivity/sounds/24096/
Credits go to acclivity
fixed effect wet_level calculation, which was accidentally turned upside down and is now working properly