Support ac3 (5.1) audio - 6 channels

[matvp91]

Sneak peak:

• I think there's a bug in HLS.js with setAudioOption, particularly at https://github.com/video-dev/hls.js/blob/master/src/utils/rendition-helper.ts#L486, where if index is 0, it'll be skipped entirely.
• When selecting a new group (eg; from aac to ac3), level selection is reset. We should preserve that, or look at HLS.js if they have some sort of logic to do it for us. Nonetheless, due to this behavior, facade thinks it's not in ABR mode when HLS.js is auto selecting quality.
• We should ship with a map of common lang to label.