Added Video hero

Displays a video inside a hero if you are on desktop and the file is set in the image node (Video field made in previous PR). Also falls back to default landscape photo if the video is not set. 

Fixes #3333 

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@aaronschachter can you sanity check what I did?

`$vars['hero_image']['video']` might not be set right?  If a notfound node doesn't have a video, this will produce an error.  Please check the error logs (http://dev.dosomething.org:8888/admin/reports/dblog) as you visit various notfound nodes with different content (with video, without) to make sure you aren't adding errors in there. http://dev.dosomething.org:8888/admin/reports/dblog