Add Multimedia - step 2 - check for captions

[kathi-fletcher]

Plugin to embed multimedia - add accessibility metadata in place

We want a multimedia embed tool that will allow video and other embedded content in the editor.
We will do this in several stages. Each stage will be a separate issue. This issue covers the second stage.
The issue covering the first stage and listing all the stages is here:

* This Stage*

1. Check whether captions are available for the video and add metadata to the embed if so. (This issue.)

Goals

• Make accessible multimedia easy to discover (by including metadata).

Mockups

editor-57.html Firefox only: To see the action

• Click the [>] symbol in the toolbar.

The mockup isn't super relevant to this issue.

Format for the embed code

• Sample video html : N

In particular, note the accessibility metadata.

Implementation Resources

• a11ymetadata API for checking captions: (http://api.a11ymetadata.org/captions/youtubeid=Y2IJb1YnAmQ/youtube/) Note that the API could disappear, so make sure to fail gracefully.

Checklist

• When embedding by URL, check the URL to see if there are captions at youtube.
• If so, add to the metadata within the figure element.
• If the API disappears, output message in the console.
• If the API disappears, just don't add the metadata, but don't inform the author or have the app
  fail in some way. That API could disappear if Benetech stops hosting it.