[TIMOB-18925] Ti.Media.Sound duration property inconsistent value types

http://docs.appcelerator.com/platform/latest/#!/api/Titanium.Media.Sound-property-duration On iOS, this is seconds; on Android it's milliseconds. Note that the time property is milliseconds (but also used to be seconds for iOS prior to 3.0: http://docs.appcelerator.com/platform/latest/#!/api/Titanium.Media.Sound-property-time)