[CDS API] Provide all available subtitle tracks

[Will Lunniss]

The API currently returns the best match subtitle track based on the users' console preference. It would be nice if all available subtitles tracks could be returned, to give the user more control. I.e. replace the current

<subtitlesUrl>/path/to/resource</subtitlesUrl>

with

<subtitlesUrls>
    <subtitlesUrl language="English" preferred="true">/path/to/resource</subitlesUrl>
    <subtitlesUrl language="Spanish">/path/to/resource</subitlesUrl>
    <subtitlesUrl language="French">/path/to/resource</subitlesUrl>
    ...
</subtitlesUrls>