Implement simple audio effects

This PR add a way to add effect to audio sources in a simple way. Using the effects is much easier than directly with BiquadFilterNode.

Usage:
```
final effect = new LowpassAudioEffect(audioManager); // Create a effect, you can also apply parameters or change same later.

source.applyEffect(effect); // Apply effect to source

source.clearEffects() // Removes all applied effects
```
Supported filters:
* Lowpass
* Highpass
* Bandpass
* Lowshelf
* Highshelf
* Peaking
* Notch
* Allpass
* Convolver, aka roll your own effect by suppling a clip with an impulse response

I also updated the sample project to include some effects to choose from. The added impule response file was released under cc by-sa.