Support Ricoh360 embeds, possibly other 360 images.

A zendesk request came in for supporting embeds of Ricoh Theta 360 images.

We might be able to adapt the method used for SceneVR to embed a single equirectangular image, although as the request noted, images will typically be larger than StoryMap's maximum upload size.

For images hosted at theta360.com we might also be able to add a media type which recognizes the URL pattern and renders an embed. Below is an example embed taken from a random Theta 360 page found online. I don't know if it'd be feasible to dynamically write a script tag like that and get the desired behavior, but logging here in case we decide to pursue it.

<blockquote data-width="500" data-height="375" class="ricoh-theta-spherical-image" >360 Photo
 Sphere example shot with Ricoh Theta--&gt;shared via Ricoh Theta app  #theta360 - <a 
href="https://theta360.com/s/Dzp" target="_blank">Spherical Image - RICOH THETA</a>
</blockquote>
<script async src="https://theta360.com/widgets.js" charset="utf-8"></script>

Start by reviewing the existing SceneVR embedding method and the media-type handling for hosted URLs. Compare those approaches with the Ricoh Theta example and determine whether the intended scope includes equirectangular uploads, theta360.com URLs, or both; done should mean a documented, working support path with an agreed test or verification method.