More UI tweaks (calls).

1. Localize video call messages.
2. Display call message previews correctly.

src/widgets/contact.jsx

@@ -71,7 +71,10 @@ class Contact extends React.Component {
 
     // The this.props.preview contains alreay shortened Drafty or string.
     let preview;
-    if (typeof this.props.preview == 'string') {
+    if (this.props.previewIsVideoCall) {
+      preview = <><i className='material-icons'>{this.props.previewIsResponse ? 'call_received' : 'call_made'}</i>
+                  <i className='material-icons'>video_call</i></>;
+    } else if (typeof this.props.preview == 'string') {
       preview = this.props.preview;
     } else if (Drafty.isValid(this.props.preview)) {
       preview = React.createElement(React.Fragment, null, Drafty.format(this.props.preview, previewFormatter,