Change gfycat siteModule behaviour to show video instead of gif.

As you point out, all RES users have html5 so we've re-thought this.

It can be the submitters choice what type of link they submit.  For an html5 video link, RES users should see video.

If someone submits a direct link to a gif from gfycat, then the preview should show gif (we wrote in a test for this, but notice RES already catches .gif and handles).