Include oEmbed data in Social Network Post embed modals

[rpeterman-gp]

Similarly to Video embeds (Issue #348), embeds for social network posts act as a 1:1 reference to data on a provider network. oEmbed data from these providers can be used to populate title data, and gather appropriate embed code markup for embedding the post. Currently the embed code we are generating for these types of embeds are incomplete, usually providing just and empty <a> tag with href pointing to the post. For distributions where javascript doesn't get run, the embed is basically useless.

What our Twitter Embed generates for tweets currently:

<blockquote class="twitter-tweet" data-lang="en">
    <a href="https://twitter.com/PRI/status/791729531602210816"></a>
</blockquote>
<scipt async src="//platform.twitter.com/widgets.js" charset="utf-8""></script>

Ideally embed code should provide usefully, readable fallback content for when javascript does not run.

Also, editing of the posts' URL's should be prevented after being saved to the platform. Changing a social post embed's URL after being saved is equivalent to removing the embed from the system and replacing it with a new one, which can have unexpected consequences in regards to the original post's usage in context with the content it was embedded into.

TODO:

• Facebook Embed
  • Prevent editing of URL after first save
  • Get oEmbed data from provider's endpoints appropriate for post type, Post or Video.
  • When oEmbed data lacks title key, parse embed HTML for title and construct a title with it and author name, if a title has not already been entered by user.
• Twitter Embed
  • Prevent editing of URL after first save
  • oEmbed data will provide embed code that is complete. Currently we are only rendering a link anchor without text of the tweet.
• Instagram Embed
  • Prevent editing of URL after first save
  • oEmbed data will provide embed code that is complete. Currently we are only rendering a link anchor without text.

If provider's oEmbed API does not support jsonp callback options, use (Noembed)[https://noembed.com/] until an in-house oEmbed API endpoint can be built. If the provider is not supported by Nombed, omit oEmbed data and generate embed code locally until either (1) the in-house oEmbed API is built, or (2) provider's oEmbed API supports jsonp callbacks.