Add expanded metadata to /articleservice API.

[tamarahills]

client will pass in a body element of v=2 to request the expanded metadata.

Here is the sample response.

[ { "format": "mp3", "url": "https://bucket.s3.amazonaws.com/sha1.mp3", "status": "available", "language": "en", "voice": "Joanna", "sample_rate": 16000, "duration": 300, "size": 5000000, }, { "format": "opus", "url": "https://bucket.s3.amazonaws.com/sha2.opus", "status": "processing", "language": "en", "voice": "Joanna", "sample_rate": 16000, "duration": 300, "size": null, } ]

1. Need to get exact duration (ffprobe)?
2. Be able to check on the status of the transcoded opus file when we already have synthesized the file.
3. Store the language?
4. Store the voice?

[tamarahills]

Fixed by #156