Add duration field to media items

[brettdh]

Motivation

All the media items (podcast episode, meditation, liturgy item) display a duration, but this is not yet part of the API spec. It could be determined from the media downloaded from the media URL, but it would be nice to be able to display this in the app before the entire file is downloaded - particularly for a podcast, where the media files can be quite large. Since we are the CMS, we can determine these when files are added, allowing the app to not worry about this calculation for every media file.

As for format: I suggest an ISO 8601 duration string (easy to handle in the app via momentjs).

Plan of action

Criteria to close

• Podcast episodes, meditations, and liturgy items return a duration attribute, which is an ISO 8601 duration string.