support header image in QuestionDialog

src/components/views/dialogs/QuestionDialog.js

@@ -31,6 +31,7 @@ export default createReactClass({
         danger: PropTypes.bool,
         focus: PropTypes.bool,
         onFinished: PropTypes.func.isRequired,
+        headerImage: PropTypes.string,
     },
 
     getDefaultProps: function() {
@@ -63,6 +64,7 @@ export default createReactClass({
             <BaseDialog className="mx_QuestionDialog" onFinished={this.props.onFinished}
                 title={this.props.title}
                 contentId='mx_Dialog_content'
+                headerImage={this.props.headerImage}
                 hasCancel={this.props.hasCancelButton}
             >
                 <div className="mx_Dialog_content" id='mx_Dialog_content'>