message: Fix one kind of scroll jump
  by calling onWidgetLoad when the <img> in MImageBody loads
diff: @@ -230,6 +230,7 @@ module.exports = React.createClass({
  <a href={contentUrl} onClick={this.onClick}>
  <img className="mx_MImageBody_thumbnail" src={thumbUrl} ref="image"
  alt={content.body}
  + onLoad={this.props.onWidgetLoad}
  onMouseEnter={this.onImageEnter}
  onMouseLeave={this.onImageLeave} />
  </a>
  