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/features/ui/containers/modal_container.jsx

@@ -9,6 +9,7 @@ import ImageLoader from 'react-imageloader';
 import LoadingIndicator from '../../../components/loading_indicator';
 import PureRenderMixin from 'react-addons-pure-render-mixin';
 import ImmutablePropTypes from 'react-immutable-proptypes';
+import ExtendedVideoPlayer from '../../../components/extended_video_player';
 
 const mapStateToProps = state => ({
   media: state.getIn(['modal', 'media']),
@@ -131,27 +132,34 @@ const Modal = React.createClass({
       return null;
     }
 
-    const url = media.get(index).get('url');
+    const attachment = media.get(index);
+    const url = attachment.get('url');
 
-    let leftNav, rightNav;
+    let leftNav, rightNav, content;
 
-    leftNav = rightNav = '';
+    leftNav = rightNav = content = '';
 
     if (media.size > 1) {
       leftNav  = <div style={leftNavStyle} className='modal-container--nav' onClick={this.handlePrevClick}><i className='fa fa-fw fa-chevron-left' /></div>;
       rightNav = <div style={rightNavStyle} className='modal-container--nav' onClick={this.handleNextClick}><i className='fa fa-fw fa-chevron-right' /></div>;
     }
 
-    return (
-      <Lightbox {...other}>
-        {leftNav}
-
+    if (attachment.get('type') === 'image') {
+      content = (
         <ImageLoader
           src={url}
           preloader={preloader}
           imgProps={{ style: imageStyle }}
         />
+      );
+    } else if (attachment.get('type') === 'gifv') {
+      content = <ExtendedVideoPlayer src={url} />;
+    }
 
+    return (
+      <Lightbox {...other}>
+        {leftNav}
+        {content}
         {rightNav}
       </Lightbox>
     );