[TIMOB-12210] iOS: Audio Ducking Support

Feature

Add support for "ducking" and "unducking" the iOS audio session. The SDK doesn't expose this right now, but it can very easily. An example of ducking is when the GPS lowers other sounds to say something, then raises them after it is done speaking.

Proposed Solution

Expose "Ti.Media.ducking = true /* or false */;". Something like the following: In TiMediaAudioSession.m:

-(void)setDucking:(UInt32)mode
{
	if ([self isActive]) {
		DebugLog(@"[WARN] Setting ducking while playing audio... changes will not take effect until audio is restarted.");
	}
	AudioSessionSetProperty(kAudioSessionProperty_OtherMixableAudioShouldDuck,sizeof(mode),&mode);
}

And in MediaModule.m:

-(void)setDucking:(NSNumber*)mode
{
    [[TiMediaAudioSession sharedSession] setDucking:[mode unsignedIntValue]];
}

Apple Documentation

Apple talks about this feature in the last paragraph on this page: http://developer.apple.com/library/ios/#documentation/Audio/Conceptual/AudioSessionProgrammingGuide/Configuration/Configuration.html