Getting audio tracks locales by parsing their ID or their label, should not be
done by clients, but by the extractor.
This commit adds the ability to store the Locale of an AudioStream, which is
used to compare similar AudioStreams (in the equalStats method).
Stream constructors are now private and streams can be constructed with new Builder classes per stream class. This change has been made to prevent creating and using several constructors in stream classes.
Some default cases have been also added in these Builder classes, so not everything has to be set, depending of the service and the content.