Fix #431 - convert gif to webm during upload. Web UI treats them like it did

before. In the API, attachments now can be either image, video or gifv. Gifv
is to be treated like images in terms of behaviour, but are videos by file
type.

app/assets/javascripts/components/components/extended_video_player.jsx

@@ -0,0 +1,21 @@
+import PureRenderMixin from 'react-addons-pure-render-mixin';
+
+const ExtendedVideoPlayer = React.createClass({
+
+  propTypes: {
+    src: React.PropTypes.string.isRequired
+  },
+
+  mixins: [PureRenderMixin],
+
+  render () {
+    return (
+      <div>
+        <video src={this.props.src} autoPlay muted loop />
+      </div>
+    );
+  },
+
+});
+
+export default ExtendedVideoPlayer;