u-video draft->core bc way more than 3+ pub and consuming impls/sites

@benwerd

It appears from http://indieweb.org/video#IndieWeb_Examples that there are way more than 3+ publishing sites that support u-video

For consuming, known implementations include:

1. Bridgy Publish supports consuming h-entry with u-video (for POSSEing to Twitter, Facebook, Flickr, e.g. this post http://tantek.com/2016/055/t12/fast-walk-hike-beach-video used Bridgy to do that)
1. Woodwind.xyz (pretty sure - need to verify it embeds video in a usable way)
Others?
** Need to determine what other kinds of u-video consuming code / libraries / applications there may be

This issue is for tracking the maturity of u-video to transition it to a core property.

Once all the "Need to" items above have been processed and resolved successfully, we should be able to move forward.

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